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Question 1:
A 12-year-old boy presents with progressive pain and swelling in his left mid-femur for three months. Radiographs show a lytic lesion with an 'onion-skin' periosteal reaction and a large soft tissue mass. Biopsy reveals small round blue cells. Which of the following genetic translocations is most characteristic of Ewing's Sarcoma?
Options:
- t(11;22)(q24;q12) EWS-FLI1
- t(X;18)(p11.2;q11.2) SYT-SSX1/2
- t(12;16)(q13;p11) FUS-DDIT3
- t(2;13)(q35;q14) PAX3-FKHR
- t(9;22)(q34;q11) BCR-ABL
Correct Answer: t(11;22)(q24;q12) EWS-FLI1
Explanation:
Ewing's Sarcoma is characterized by specific chromosomal translocations involving the EWSR1 gene on chromosome 22, most commonly fused with the FLI1 gene on chromosome 11, resulting in the t(11;22)(q24;q12) EWS-FLI1 fusion protein. This fusion acts as an aberrant transcription factor crucial for oncogenesis. The other options are characteristic translocations for Synovial Sarcoma (t(X;18)), Myxoid Liposarcoma (t(12;16)), Alveolar Rhabdomyosarcoma (t(2;13)), and Chronic Myeloid Leukemia (t(9;22)), respectively.
Question 2:
Regarding the clinical presentation of Ewing's Sarcoma, which of the following statements is most accurate?
Options:
- It typically presents in older adults, often mistaken for metastatic carcinoma.
- Pain, localized swelling, and constitutional symptoms like fever and weight loss are common, particularly in adolescents and young adults.
- It primarily affects the epiphyseal regions of long bones, mimicking chondroblastoma.
- Pathologic fractures are rare and usually indicate a benign etiology.
- The most common site of presentation is the small bones of the hands and feet.
Correct Answer: Pain, localized swelling, and constitutional symptoms like fever and weight loss are common, particularly in adolescents and young adults.
Explanation:
Ewing's Sarcoma typically affects children, adolescents, and young adults (peak incidence between 10-20 years). Pain, often worse at night, and localized swelling are hallmark symptoms. Constitutional symptoms such as fever, malaise, weight loss, and elevated inflammatory markers (ESR, CRP) can occur, mimicking infection. It commonly affects the diaphysis and metaphysis of long bones and flat bones like the pelvis, ribs, and scapula, not typically the epiphysis. Pathologic fractures are not rare and can be the initial presentation, though they may complicate diagnosis. The small bones of the hands and feet are less common sites.
Question 3:
A 10-year-old girl is diagnosed with Ewing's Sarcoma of the proximal tibia. What is the most critical imaging modality for accurate local staging and surgical planning?
Options:
- Plain Radiographs (X-rays)
- Computed Tomography (CT) scan of the chest
- Bone Scan (Technetium-99m)
- Magnetic Resonance Imaging (MRI) with contrast of the affected limb
- Positron Emission Tomography (PET) scan
Correct Answer: Magnetic Resonance Imaging (MRI) with contrast of the affected limb
Explanation:
MRI with contrast is the gold standard for local staging of bone and soft tissue tumors, including Ewing's Sarcoma. It provides superior soft tissue resolution, allowing accurate assessment of intramedullary and extraosseous tumor extent, involvement of neurovascular bundles, joint invasion, and skips lesions, all crucial for surgical planning and determining resectability. Plain radiographs are initial screening tools, CT chest is for lung metastases, bone scan for skeletal metastases, and PET scan for systemic staging and response assessment, but MRI is paramount for local evaluation.
Question 4:
Which immunohistochemical marker is highly sensitive, though not entirely specific, for the diagnosis of Ewing's Sarcoma?
Options:
- S-100 protein
- Desmin
- CD31
- CD99 (MIC2)
- Cytokeratin
Correct Answer: CD99 (MIC2)
Explanation:
CD99 (MIC2 gene product) is expressed in over 90% of Ewing's Sarcomas, showing a characteristic diffuse membranous staining pattern. While sensitive, it is not specific as it can also be seen in lymphoblastic lymphoma, some rhabdomyosarcomas, and synovial sarcomas. S-100 is positive in neural and cartilaginous tumors, Desmin in muscle tumors (rhabdomyosarcoma), CD31 in endothelial tumors, and Cytokeratin in epithelial tumors (carcinomas) and synovial sarcoma.
Question 5:
A 15-year-old male with Ewing's Sarcoma of the ilium has completed neoadjuvant chemotherapy. What is the standard approach for definitive local control in a resectable pelvic Ewing's Sarcoma?
Options:
- Radiation therapy alone
- Amputation, regardless of resectability
- Surgical resection with wide margins, often combined with adjuvant radiation therapy
- Continuation of chemotherapy for 12 months without local treatment
- Percutaneous cryoablation
Correct Answer: Surgical resection with wide margins, often combined with adjuvant radiation therapy
Explanation:
For resectable Ewing's Sarcoma, particularly in the pelvis where achieving wide surgical margins can be challenging, definitive local control typically involves surgical resection with wide margins, often complemented by adjuvant radiation therapy, especially if margins are close or positive. Pelvic tumors have historically been difficult to treat, but multimodal therapy with aggressive surgery and radiation has improved outcomes. Radiation alone is reserved for unresectable tumors or those with gross residual disease after surgery. Amputation is generally reserved for unresectable extremity tumors or extensive local recurrence. Percutaneous cryoablation is not a standard definitive treatment for large, aggressive tumors like Ewing's.
Question 6:
Which of the following is considered the most important negative prognostic factor in a patient diagnosed with Ewing's Sarcoma?
Options:
- Age greater than 10 years
- Tumor size less than 8 cm
- Primary tumor site in the distal extremity
- Presence of metastatic disease at diagnosis
- Elevated LDH
Correct Answer: Presence of metastatic disease at diagnosis
Explanation:
The presence of metastatic disease at diagnosis is the single most important negative prognostic factor in Ewing's Sarcoma. Patients with metastatic disease have significantly worse survival rates compared to those with localized disease. While other factors like large tumor size, central axial location (pelvis, spine), poor response to neoadjuvant chemotherapy, and elevated LDH are also poor prognostic indicators, metastatic disease portends the gravest prognosis.
Question 7:
The classic radiographic appearance of Ewing's Sarcoma in long bones is characterized by:
Options:
- Dense sclerotic lesion with sunburst periosteal reaction
- Epiphyseal lytic lesion with a geographic border
- Diaphyseal lytic lesion with an 'onion-skin' periosteal reaction and a large soft tissue component
- Metaphyseal lesion with a 'falling leaf' sign on MRI
- Well-defined cortical defect with internal calcifications
Correct Answer: Diaphyseal lytic lesion with an 'onion-skin' periosteal reaction and a large soft tissue component
Explanation:
Ewing's Sarcoma typically manifests as a diaphyseal or metadiaphyseal lytic lesion, often with ill-defined margins. The characteristic periosteal reaction is lamellated or 'onion-skin' due to layers of reactive bone formation. A significant soft tissue mass, often larger than the intraosseous component, is almost always present. Sclerotic lesions with sunburst reactions are more typical of osteosarcoma. Epiphyseal lesions are characteristic of chondroblastoma. The 'falling leaf' sign is not typical, and well-defined cortical defects with calcifications describe conditions like osteochondroma or fibrous cortical defects, not Ewing's.
Question 8:
A patient with Ewing's Sarcoma presents with a pathological fracture of the femur. What is the appropriate initial management strategy?
Options:
- Immediate surgical stabilization and definitive resection
- Radiation therapy to the fracture site followed by chemotherapy
- Initiation of neoadjuvant chemotherapy, with fracture stabilization if symptomatic or unstable
- Amputation as the primary treatment due to poor prognosis
- Observation with close monitoring, avoiding surgical intervention
Correct Answer: Initiation of neoadjuvant chemotherapy, with fracture stabilization if symptomatic or unstable
Explanation:
For a pathological fracture in Ewing's Sarcoma, the initial management prioritizes systemic disease control. Neoadjuvant chemotherapy should be initiated promptly to treat potential micrometastases and achieve tumor regression. Fracture stabilization (e.g., intramedullary nailing) is performed if the fracture causes significant pain or instability, or if it delays chemotherapy. Definitive surgical resection is typically planned after chemotherapy. Immediate definitive resection is often not ideal due to the risk of tumor dissemination and the need for systemic therapy first. Amputation is a last resort, and observation is inappropriate for an aggressive tumor with a pathological fracture.
Question 9:
Which of the following is a recognized late complication of radiation therapy used in the treatment of Ewing's Sarcoma, particularly in pediatric patients?
Options:
- Cardiotoxicity
- Nephrotoxicity
- Secondary malignancies
- Peripheral neuropathy
- Hemorrhagic cystitis
Correct Answer: Secondary malignancies
Explanation:
Secondary malignancies (e.g., osteosarcoma, thyroid cancer, leukemia) are a significant late complication of radiation therapy, especially in growing children, due to radiation-induced DNA damage. Other late effects include growth plate arrest leading to limb length discrepancy, scoliosis (for spinal irradiation), joint stiffness, and soft tissue fibrosis. Cardiotoxicity (e.g., from doxorubicin), nephrotoxicity (e.g., from ifosfamide), peripheral neuropathy (e.g., from vincristine), and hemorrhagic cystitis (e.g., from cyclophosphamide/ifosfamide) are typically associated with chemotherapy, not radiation directly.
Question 10:
A 14-year-old girl is found to have Ewing's Sarcoma of the sacrum. Given the location, what is a primary concern regarding surgical resection?
Options:
- Risk of pulmonary metastasis
- Preservation of adjacent growth plates
- Difficulty in achieving wide surgical margins and potential neurological deficits
- Increased likelihood of developing osteonecrosis
- Early development of pathologic fracture
Correct Answer: Difficulty in achieving wide surgical margins and potential neurological deficits
Explanation:
Sacral Ewing's Sarcoma presents significant challenges for surgical resection. The complex anatomy, proximity to critical neurovascular structures (sacral nerve roots, rectum, bladder), and the difficulty in achieving wide tumor-free margins without causing severe functional impairment (e.g., bladder/bowel incontinence, motor/sensory deficits) are primary concerns. Pulmonary metastasis is a systemic staging issue, not a direct surgical concern for local control. Preservation of growth plates is more relevant for extremity tumors in younger patients. Osteonecrosis is a potential complication of radiation or steroid use, not specific to sacral surgery. Pathologic fracture risk exists but is not the primary surgical concern for *resection* challenges.
Question 11:
What is the typical age range for the highest incidence of Ewing's Sarcoma?
Options:
- Infancy (0-2 years)
- Preschool children (3-5 years)
- Adolescents and young adults (10-20 years)
- Middle-aged adults (40-60 years)
- Elderly individuals (>70 years)
Correct Answer: Adolescents and young adults (10-20 years)
Explanation:
Ewing's Sarcoma is predominantly a tumor of childhood and adolescence, with the highest incidence occurring in individuals between 10 and 20 years of age. It is rare in infants and older adults, though cases outside this typical range do occur.
Question 12:
A core biopsy confirms Ewing's Sarcoma. Which additional diagnostic procedure is essential for initial staging to detect metastatic disease?
Options:
- Electromyography (EMG) of the affected limb
- Arteriogram of the tumor site
- Bone marrow aspiration and biopsy
- Myelogram if the tumor is spinal
- Doppler ultrasound of regional lymph nodes
Correct Answer: Bone marrow aspiration and biopsy
Explanation:
Ewing's Sarcoma has a high propensity for micrometastasis, and common sites include the lungs, bone, and bone marrow. Therefore, a bone marrow aspiration and biopsy is a crucial component of the initial staging workup to detect bone marrow involvement, which affects prognosis and treatment decisions. CT chest, bone scan, and/or PET-CT are also essential for evaluating other metastatic sites. The other options are not standard for initial systemic staging.
Question 13:
Regarding the differential diagnosis of Ewing's Sarcoma, which tumor shares the 'small round blue cell' histological appearance and must be differentiated?
Options:
- Osteosarcoma
- Chondrosarcoma
- Fibrosarcoma
- Rhabdomyosarcoma
- Giant Cell Tumor of Bone
Correct Answer: Rhabdomyosarcoma
Explanation:
Ewing's Sarcoma is classically described as a 'small round blue cell tumor.' Other tumors that fall into this category and must be differentiated include Rhabdomyosarcoma, Lymphoma, Neuroblastoma, and occasionally Primitive Neuroectodermal Tumor (PNET), which is now considered part of the Ewing's sarcoma family of tumors. Osteosarcoma and chondrosarcoma are typically spindle cell or cartilaginous tumors, respectively. Fibrosarcoma is a spindle cell tumor, and Giant Cell Tumor is characterized by multinucleated giant cells and mononuclear stromal cells.
Question 14:
Which of the following chemotherapy agents is NOT typically part of the standard multi-agent regimen for Ewing's Sarcoma?
Options:
- Vincristine
- Doxorubicin
- Cyclophosphamide
- Methotrexate (high dose)
- Ifosfamide
Correct Answer: Methotrexate (high dose)
Explanation:
The standard chemotherapy regimen for Ewing's Sarcoma commonly includes Vincristine, Doxorubicin, Cyclophosphamide, Ifosfamide, and Etoposide (often abbreviated as VDC/IE). High-dose methotrexate is a key agent in osteosarcoma chemotherapy but is not a standard component of Ewing's Sarcoma regimens. While other agents might be used in specific circumstances or relapse, the core drugs are as listed.
Question 15:
What is the typical effect of effective neoadjuvant chemotherapy on a Ewing's Sarcoma tumor?
Options:
- Increased tumor vascularity and rapid growth
- Softening of the tumor, reduction in size, and consolidation of the periosteal reaction
- Increased tumor cellularity and mitotic activity
- Conversion of a lytic lesion to a purely blastic lesion on X-ray
- Development of new skip lesions distant from the primary tumor
Correct Answer: Softening of the tumor, reduction in size, and consolidation of the periosteal reaction
Explanation:
Effective neoadjuvant chemotherapy aims to reduce tumor size (debulking), improve resectability, decrease tumor burden, and treat micrometastases. Radiographically, this often translates to a reduction in the soft tissue component, consolidation or remodeling of the periosteal reaction, and a decrease in the lytic activity, sometimes with increased sclerosis. Histologically, it leads to tumor necrosis. Increased vascularity or growth, increased cellularity, or new skip lesions would indicate treatment failure or progression.
Question 16:
A 7-year-old child undergoes limb salvage surgery for Ewing's Sarcoma of the distal femur. What is a primary long-term concern related to growth in this patient?
Options:
- Increased risk of deep vein thrombosis
- Development of significant limb length discrepancy
- Accelerated growth of the contralateral limb
- Premature fusion of all growth plates
- Development of Charcot arthropathy
Correct Answer: Development of significant limb length discrepancy
Explanation:
In growing children undergoing limb salvage surgery, particularly around long bones like the distal femur, removing or irradiating a significant portion of the growth plate or replacing it with an endoprosthesis that does not grow can lead to substantial limb length discrepancy over time. This requires careful planning, sometimes using expandable prostheses, or subsequent lengthening procedures. DVT is an acute surgical complication, not a long-term growth issue. Accelerated growth of the contralateral limb is not a direct consequence. Premature fusion of all growth plates is too general. Charcot arthropathy is a neuropathic joint condition, unrelated to growth after Ewing's surgery.
Question 17:
Which gene fusion is considered diagnostic for Ewing's sarcoma family of tumors?
Options:
- BCR-ABL
- MYC-IG
- EWSR1-FLI1
- ALK rearrangement
- RET rearrangement
Correct Answer: EWSR1-FLI1
Explanation:
The EWSR1-FLI1 fusion (most commonly t(11;22)) is the defining genetic hallmark of Ewing's Sarcoma and related tumors (Ewing Sarcoma family of tumors, ESFT). While there are other EWSR1 gene partners (e.g., ERG, FEV, ETV1), EWSR1-FLI1 is the most prevalent. BCR-ABL is associated with CML, MYC-IG with Burkitt lymphoma, ALK rearrangement with anaplastic large cell lymphoma and non-small cell lung cancer, and RET rearrangement with papillary thyroid cancer and other neoplasms.
Question 18:
During the evaluation of a suspected Ewing's Sarcoma, what is the role of a CT scan of the chest?
Options:
- To assess local tumor extent and bone involvement in the primary site
- To detect pulmonary metastases, which are common at diagnosis
- To evaluate neurological deficits related to spinal involvement
- To identify skip lesions in the affected extremity
- To quantify tumor necrosis after chemotherapy
Correct Answer: To detect pulmonary metastases, which are common at diagnosis
Explanation:
CT scan of the chest is an essential part of the initial staging for Ewing's Sarcoma to detect pulmonary metastases. The lungs are the most common site of metastasis at diagnosis, accounting for approximately 25-30% of cases. MRI is preferred for local tumor extent, CT or MRI for spinal involvement, and MRI for skip lesions. Quantification of tumor necrosis is typically done histologically after resection.
Question 19:
The presence of a 'small round blue cell tumor' on biopsy requires differentiation from several entities. Besides immunohistochemistry, what specialized test confirms Ewing's Sarcoma?
Options:
- Electron microscopy for Birbeck granules
- Fluorescence In Situ Hybridization (FISH) for EWSR1 gene rearrangement
- Enzyme-linked immunosorbent assay (ELISA) for tumor markers
- Flow cytometry for surface markers
- Immunophenotyping for T-cell receptors
Correct Answer: Fluorescence In Situ Hybridization (FISH) for EWSR1 gene rearrangement
Explanation:
Given the characteristic genetic translocations, Fluorescence In Situ Hybridization (FISH) for the EWSR1 gene rearrangement (e.g., EWSR1-FLI1) is a highly specific and definitive test for confirming the diagnosis of Ewing's Sarcoma. Electron microscopy for Birbeck granules is for Langerhans cell histiocytosis. ELISA is for circulating markers. Flow cytometry and immunophenotyping are primarily used for hematolymphoid malignancies.
Question 20:
What is the primary role of high-dose chemotherapy with autologous stem cell rescue in the management of Ewing's Sarcoma?
Options:
- Routine frontline treatment for all localized Ewing's Sarcomas
- Standard treatment for low-risk localized disease
- Salvage therapy for recurrent or high-risk metastatic disease
- Prevention of chemotherapy-induced neuropathy
- Primary treatment for isolated pulmonary metastases
Correct Answer: Salvage therapy for recurrent or high-risk metastatic disease
Explanation:
High-dose chemotherapy with autologous stem cell rescue is typically reserved for patients with recurrent Ewing's Sarcoma or those with high-risk metastatic disease at diagnosis, particularly if they have a good response to conventional chemotherapy. It is not a routine frontline treatment for all localized disease due to significant toxicity. It is a salvage strategy to intensify treatment beyond what can be delivered without stem cell support.
Question 21:
Which statement regarding the role of surgical margins in Ewing's Sarcoma is correct?
Options:
- Marginal resections are acceptable due to the efficacy of adjuvant chemotherapy.
- Intralesional resections are curative if followed by radiation therapy.
- Wide surgical margins (R0 resection) are associated with the best local control and overall survival.
- Positive surgical margins (R1 resection) are always treated with amputation.
- Biopsy-only is sufficient if chemotherapy achieves complete response.
Correct Answer: Wide surgical margins (R0 resection) are associated with the best local control and overall survival.
Explanation:
Achieving wide surgical margins, leading to an R0 resection (no microscopic tumor at the margin), is a critical prognostic factor for local control and overall survival in Ewing's Sarcoma. While chemotherapy and radiation are vital components of multimodal therapy, negative surgical margins significantly reduce the risk of local recurrence. Marginal or intralesional resections without clear margins carry a higher risk of recurrence and usually necessitate adjuvant radiation. Positive margins do not automatically lead to amputation but require further local treatment, often radiation, and sometimes re-excision.
Question 22:
A patient with Ewing's Sarcoma of the femur develops severe myelosuppression during chemotherapy. Which of the following is the most appropriate management strategy?
Options:
- Immediate cessation of all chemotherapy
- Increase the dosage of the current chemotherapy agents
- Administration of granulocyte colony-stimulating factors (G-CSFs) and potential dose reductions or delays
- Switch to a completely different chemotherapy regimen immediately
- Surgical removal of bone marrow
Correct Answer: Administration of granulocyte colony-stimulating factors (G-CSFs) and potential dose reductions or delays
Explanation:
Myelosuppression (bone marrow suppression) is a common and dose-limiting toxicity of chemotherapy, particularly with agents used in Ewing's Sarcoma. Management typically involves supportive care, including the administration of granulocyte colony-stimulating factors (G-CSFs) to promote white blood cell recovery, and if severe, temporary dose reductions or delays in chemotherapy cycles to allow for marrow recovery. Complete cessation of chemotherapy or increasing dosages would be inappropriate. Switching regimens is usually reserved for non-response or specific toxicities, not routine myelosuppression. Surgical removal of bone marrow is irrelevant.
Question 23:
What is the significance of serum LDH (Lactate Dehydrogenase) levels in Ewing's Sarcoma?
Options:
- It is a specific diagnostic marker for Ewing's Sarcoma.
- Elevated levels correlate with a better prognosis and response to treatment.
- It is a non-specific marker, but elevated levels often indicate a higher tumor burden and poorer prognosis.
- LDH levels are only elevated in the presence of liver metastases.
- It is used to monitor the effectiveness of local radiation therapy.
Correct Answer: It is a non-specific marker, but elevated levels often indicate a higher tumor burden and poorer prognosis.
Explanation:
Serum LDH is a non-specific tumor marker that can be elevated in various cancers, including Ewing's Sarcoma. While not diagnostic, elevated LDH levels at diagnosis in Ewing's Sarcoma are generally considered a poor prognostic indicator, often correlating with higher tumor burden, more aggressive disease, and a worse outcome. It is not specific to liver metastases, nor does it typically monitor local radiation effectiveness.
Question 24:
Extraskeletal Ewing's Sarcoma most commonly arises in which location?
Options:
- Brain parenchyma
- Spinal cord
- Kidney
- Soft tissues of the trunk and extremities
- Thyroid gland
Correct Answer: Soft tissues of the trunk and extremities
Explanation:
Extraskeletal Ewing's Sarcoma is a rare variant that arises in soft tissues without primary bone involvement. The most common sites are the soft tissues of the trunk and extremities, including paravertebral regions, chest wall, retroperitoneum, and deep soft tissues of the limbs. Brain, spinal cord, kidney, and thyroid are rare or atypical primary sites for extraskeletal Ewing's.
Question 25:
A 16-year-old male presents with back pain, leg weakness, and a sacral mass. Biopsy confirms Ewing's Sarcoma. What is the immediate concern for neurological function?
Options:
- Risk of peripheral neuropathy from chemotherapy
- Imminent spinal cord compression
- Ischemic stroke
- Hydrocephalus
- Cerebellar dysfunction
Correct Answer: Imminent spinal cord compression
Explanation:
A sacral mass with leg weakness points to potential spinal cord or cauda equina compression, which is an oncologic emergency requiring urgent evaluation (MRI spine) and often emergent treatment (radiation or surgical decompression) to preserve neurological function. Peripheral neuropathy is a side effect of certain chemotherapeutic agents (e.g., vincristine) but not an immediate concern related to the mass itself. The other options are not directly related to a sacral mass with leg weakness.
Question 26:
What is the recommended surveillance schedule for patients after completion of Ewing's Sarcoma treatment?
Options:
- Annual follow-up with plain radiographs only for 5 years.
- Clinical exam, chest imaging (CT or X-ray), and blood tests every 3-4 months for the first 2-3 years, then less frequently.
- Monthly MRI scans of the primary site for 1 year.
- No further follow-up is needed after 2 years if no recurrence.
- Bone scan every 6 months indefinitely.
Correct Answer: Clinical exam, chest imaging (CT or X-ray), and blood tests every 3-4 months for the first 2-3 years, then less frequently.
Explanation:
Post-treatment surveillance for Ewing's Sarcoma is crucial for detecting recurrence or secondary malignancies. A typical schedule involves frequent clinical exams, chest imaging (CT or X-ray for pulmonary mets), and blood tests (including LDH) every 3-4 months for the first 2-3 years, when the risk of recurrence is highest. The frequency then decreases to every 6 months for another 2-3 years, and then annually for several more years. MRI of the primary site is usually done less frequently than monthly. No follow-up after 2 years is insufficient. Bone scans are used if new bone symptoms arise, not routinely every 6 months indefinitely.
Question 27:
Which finding on a follow-up PET-CT scan after completion of Ewing's Sarcoma treatment would be most concerning for recurrence?
Options:
- Stable mild FDG uptake in a known benign cyst
- Diffuse low-grade FDG uptake in the liver
- New focal area of intense FDG avidity in the vertebral body distant from the primary site
- Physiologic FDG uptake in the brain
- Decreased FDG uptake in an area of post-radiation fibrosis
Correct Answer: New focal area of intense FDG avidity in the vertebral body distant from the primary site
Explanation:
PET-CT detects metabolically active tissue. A new focal area of intense FDG avidity in a vertebral body (or any new site) would be highly suspicious for a new bone metastasis, indicating disease recurrence, especially if distant from the primary site. Stable mild uptake in a benign lesion, diffuse low-grade uptake, physiologic uptake, or decreased uptake in fibrosis are typically benign or expected post-treatment findings.
Question 28:
When considering radiation therapy for Ewing's Sarcoma, what is the primary indication for its use in conjunction with surgery?
Options:
- As a substitute for systemic chemotherapy
- To prevent limb length discrepancy in children
- To sterilize positive or close surgical margins and treat unresectable disease
- To increase bone density in the treated area
- To induce a pathologic fracture for easier resection
Correct Answer: To sterilize positive or close surgical margins and treat unresectable disease
Explanation:
Radiation therapy is a critical component of multimodal treatment for Ewing's Sarcoma. Its primary indications are to improve local control in cases where surgical margins are positive or close (R1 or R2 resection), or when the tumor is unresectable. It is never a substitute for systemic chemotherapy, which addresses micrometastases. It does not prevent limb length discrepancy (it can cause it), nor does it increase bone density or induce fractures for easier resection.
Question 29:
Which characteristic typically distinguishes Ewing's Sarcoma from osteosarcoma on a plain radiograph?
Options:
- Ewing's often presents with an 'onion-skin' periosteal reaction, while osteosarcoma commonly shows a 'sunburst' or Codman's triangle.
- Ewing's is usually a purely sclerotic lesion, while osteosarcoma is purely lytic.
- Ewing's primarily affects the epiphysis, whereas osteosarcoma affects the diaphysis.
- Ewing's lesions typically have sharp, well-defined margins, unlike osteosarcoma.
- Osteosarcoma rarely has a soft tissue mass, while Ewing's always does.
Correct Answer: Ewing's often presents with an 'onion-skin' periosteal reaction, while osteosarcoma commonly shows a 'sunburst' or Codman's triangle.
Explanation:
Ewing's Sarcoma classically presents with a lamellated ('onion-skin') periosteal reaction due to its rapid, infiltrative growth pattern. Osteosarcoma, in contrast, frequently demonstrates a 'sunburst' periosteal reaction (spicules perpendicular to the cortex) or a Codman's triangle (triangular elevation of the periosteum). Ewing's is typically lytic, and osteosarcoma can be lytic, sclerotic, or mixed. Ewing's usually affects diaphysis/metadiaphysis, while osteosarcoma typically affects the metaphysis. Both often have poorly defined margins and a significant soft tissue mass.
Question 30:
What is the primary goal of neoadjuvant (pre-operative) chemotherapy in Ewing's Sarcoma?
Options:
- To avoid the need for surgery completely.
- To improve patient nutrition before surgery.
- To reduce tumor size, treat micrometastatic disease, and assess tumor response.
- To definitively cure the local tumor without any further treatment.
- To induce a pathological fracture for easier tumor removal.
Correct Answer: To reduce tumor size, treat micrometastatic disease, and assess tumor response.
Explanation:
The primary goals of neoadjuvant chemotherapy in Ewing's Sarcoma are to reduce the primary tumor size (making surgical resection easier and potentially limb-sparing), to eradicate micrometastatic disease (which is often present at diagnosis even if not detectable), and to assess the tumor's chemosensitivity, which has prognostic implications. It is rarely intended to completely avoid surgery or achieve definitive local cure alone.
Question 31:
In the context of Ewing's Sarcoma, what does 'PNET' refer to?
Options:
- Primary Neural Exudative Tumor
- Peripheral Neuroectodermal Tissue
- Primitive Neuroectodermal Tumor
- Post-Neoplastic Endothelial Thrombosis
- Pulmonary Nodule Etiology Testing
Correct Answer: Primitive Neuroectodermal Tumor
Explanation:
PNET stands for Primitive Neuroectodermal Tumor. Historically, PNETs were considered a separate but related entity to Ewing's Sarcoma, often exhibiting more neuroectodermal differentiation. However, with advances in molecular diagnostics, both Ewing's Sarcoma and PNET are now recognized as part of the 'Ewing Sarcoma Family of Tumors' (ESFT) due to sharing the same characteristic EWSR1 gene translocations and biological properties. The term 'Ewing's Sarcoma' is now often used inclusively for all tumors in this family.
Question 32:
A 13-year-old with Ewing's Sarcoma of the humerus is completing chemotherapy. An MRI shows residual tumor within the bone. What is the most appropriate next step for local control?
Options:
- Continue chemotherapy indefinitely until complete resolution.
- Perform surgical resection of the residual tumor, possibly with adjuvant radiation.
- Treat with high-dose steroids to shrink the residual tumor.
- Monitor with serial MRIs every month without intervention.
- Perform a repeat biopsy and restart a different chemotherapy regimen.
Correct Answer: Perform surgical resection of the residual tumor, possibly with adjuvant radiation.
Explanation:
After neoadjuvant chemotherapy, residual tumor requires definitive local treatment. For a resectable lesion like in the humerus, surgical resection with negative margins is the preferred option. Depending on the achieved margins and tumor response, adjuvant radiation therapy may also be indicated. Continuing chemotherapy indefinitely is not standard, steroids are not definitive treatment, observation is inappropriate for residual disease, and a repeat biopsy and new chemotherapy are typically for progression or relapse, not for residual tumor after planned neoadjuvant therapy.
Question 33:
Which of the following describes the typical histological appearance of Ewing's Sarcoma?
Options:
- Abundant osteoid production with spindle cells
- Large pleomorphic cells with prominent nucleoli arranged in a herringbone pattern
- Sheets of small, round, uniform cells with scant cytoplasm, often glycogen-rich
- Chondroid matrix with entrapped lacunae
- Multinucleated giant cells and mononuclear stromal cells
Correct Answer: Sheets of small, round, uniform cells with scant cytoplasm, often glycogen-rich
Explanation:
Ewing's Sarcoma is a 'small round blue cell tumor.' Histologically, it consists of sheets of relatively uniform, small, round cells with scant, clear cytoplasm (due to high glycogen content, which can be demonstrated by PAS staining) and ill-defined cell borders. Nuclei are often round to oval with fine chromatin and inconspicuous nucleoli. Abundant osteoid is seen in osteosarcoma, pleomorphic cells in undifferentiated pleomorphic sarcoma, chondroid matrix in chondrosarcoma, and giant cells in giant cell tumor.
Question 34:
Which skeletal location for Ewing's Sarcoma is generally associated with a poorer prognosis due to challenges in achieving adequate surgical margins and higher rates of recurrence?
Options:
- Distal femur
- Proximal tibia
- Ribs
- Phalanges of the hand
- Pelvis
Correct Answer: Pelvis
Explanation:
Pelvic Ewing's Sarcomas are notoriously challenging due to the complex anatomy, proximity to vital structures (sacral nerves, bladder, rectum), and the difficulty in obtaining wide, tumor-free surgical margins. This often results in higher rates of local recurrence and generally a poorer prognosis compared to extremity tumors, even with multimodal treatment. Distal femur, proximal tibia, ribs, and phalanges, while serious, often allow for more straightforward surgical resections with clearer margins.
Question 35:
Which investigation is crucial for detecting skip lesions and assessing the full intraosseous extent of Ewing's Sarcoma in a long bone?
Options:
- Plain X-ray
- CT scan of the primary site
- Bone scintigraphy (bone scan)
- MRI of the entire involved bone and adjacent joint
- Ultrasound
Correct Answer: MRI of the entire involved bone and adjacent joint
Explanation:
MRI of the entire involved bone, extending from joint to joint and including the adjacent joints, is essential for accurately assessing the intramedullary extent of the tumor, its relationship to growth plates, neurovascular structures, and for detecting 'skip lesions' (discontinuous tumor foci within the same bone). Plain X-rays and CT scans provide less detailed information about marrow involvement and soft tissue extension. Bone scans detect metabolic activity but lack anatomical detail for precise local staging. Ultrasound is primarily for soft tissue masses.
Question 36:
A 10-year-old presents with a diaphyseal femur lesion, fever, and elevated ESR. What is the most important initial step in differentiating Ewing's Sarcoma from osteomyelitis?
Options:
- Start empiric antibiotics for suspected osteomyelitis.
- Perform an open biopsy immediately.
- Obtain an MRI of the affected limb and a core needle biopsy.
- Monitor symptoms and repeat X-rays in 4-6 weeks.
- Order a white blood cell count and C-reactive protein only.
Correct Answer: Obtain an MRI of the affected limb and a core needle biopsy.
Explanation:
Ewing's Sarcoma can mimic osteomyelitis both clinically (pain, fever, elevated inflammatory markers) and radiographically. The most important initial step is to perform an MRI to better characterize the lesion and then a core needle biopsy to obtain tissue for definitive diagnosis (histology, immunohistochemistry, molecular genetics). Starting empiric antibiotics without a diagnosis risks delaying cancer treatment. Open biopsy is more invasive than core needle biopsy and typically not the first biopsy choice. Monitoring symptoms or just blood tests is insufficient given the potential for malignancy.
Question 37:
What is the typical long-term consequence of radiation therapy to a long bone in a prepubescent child for Ewing's Sarcoma?
Options:
- Increased bone density in the irradiated field.
- Accelerated growth of the treated limb.
- Growth arrest leading to limb length discrepancy and skeletal deformities.
- Increased risk of osteoporosis.
- Improved joint mobility and reduced pain.
Correct Answer: Growth arrest leading to limb length discrepancy and skeletal deformities.
Explanation:
Radiation therapy, particularly in growing children, can damage the physeal growth plates, leading to premature growth arrest in the irradiated bone segment. This commonly results in limb length discrepancies, angular deformities, and other skeletal abnormalities, requiring orthopedic management. It does not increase bone density, accelerate growth, or typically improve joint mobility long-term.
Question 38:
Which of the following describes the most common type of translocation seen in Ewing's Sarcoma?
Options:
- Reciprocal translocation involving chromosomes 11 and 22
- Deletion of a segment on chromosome 13
- Duplication of the entire chromosome 8
- Inversion within chromosome 17
- Translocation between chromosomes 9 and 22 without EWSR1 involvement
Correct Answer: Reciprocal translocation involving chromosomes 11 and 22
Explanation:
The most common translocation in Ewing's Sarcoma is the reciprocal translocation t(11;22)(q24;q12), which results in the fusion of the EWSR1 gene on chromosome 22 with the FLI1 gene on chromosome 11. Other translocations involve EWSR1 with different partners, but t(11;22) is the defining and most frequent event. The other options describe genetic anomalies not typical of Ewing's Sarcoma.
Question 39:
Which factor generally correlates with a more favorable prognosis in patients with localized Ewing's Sarcoma?
Options:
- Tumor volume greater than 200 ml
- Primary tumor in the pelvis
- Poor histologic response (less than 90% necrosis) to neoadjuvant chemotherapy
- Complete surgical resection with wide, negative margins (R0)
- Elevated baseline C-reactive protein (CRP)
Correct Answer: Complete surgical resection with wide, negative margins (R0)
Explanation:
Complete surgical resection with wide, negative margins (R0) is a crucial factor for achieving local control and is strongly associated with a more favorable prognosis in localized Ewing's Sarcoma. Conversely, large tumor volume, pelvic primary sites, and poor histologic response to chemotherapy (indicating chemoresistance) are all associated with a poorer prognosis. Elevated CRP, like LDH, is a non-specific inflammatory marker that can indicate more aggressive disease and is generally a poor prognostic sign.
Question 40:
A 9-year-old child with Ewing's Sarcoma of the femur undergoes limb salvage surgery. What type of reconstruction would typically be considered to account for future growth?
Options:
- Arthrodesis with allograft
- Custom non-expandable endoprosthesis
- Resection with fibular autograft and no further intervention
- Expandable endoprosthesis or allograft-prosthesis composite with planned lengthening procedures
- Amputation with immediate prosthetic fitting
Correct Answer: Expandable endoprosthesis or allograft-prosthesis composite with planned lengthening procedures
Explanation:
For growing children with limb salvage, techniques that address future growth are critical. Expandable endoprostheses (which can be lengthened externally without repeat surgery) or allograft-prosthesis composites often combined with planned lengthening procedures are utilized to manage limb length discrepancy as the child grows. Non-expandable prostheses or arthrodesis would result in significant limb length discrepancy. Fibular autografts alone for large defects are often insufficient, and amputation is generally a last resort.
Question 41:
What is the primary concern when considering neoadjuvant chemotherapy for an extensive pelvic Ewing's Sarcoma in a 14-year-old patient?
Options:
- The chemotherapy will delay the definitive diagnosis.
- The risk of chemotherapy-induced hypertension.
- The potential for inadequate tumor response and subsequent surgical challenges.
- Chemotherapy may cause immediate pathological fracture.
- The impact on cosmetic appearance of the skin.
Correct Answer: The potential for inadequate tumor response and subsequent surgical challenges.
Explanation:
For extensive pelvic Ewing's, neoadjuvant chemotherapy is crucial to reduce tumor burden and facilitate resection. The primary concern is the potential for inadequate tumor response, which would not only indicate a resistant tumor but also make subsequent surgical resection extremely difficult, potentially leading to positive margins, high morbidity, or even unresectability. Diagnosis is established via biopsy before starting chemotherapy. Hypertension is not a primary concern with standard regimens. While pathological fractures can occur, they are not a *primary* concern of chemotherapy itself but rather tumor progression or bone weakening. Cosmetic appearance is a lesser concern.
Question 42:
Which finding on gross pathological examination of a resected Ewing's Sarcoma specimen would indicate a good response to neoadjuvant chemotherapy?
Options:
- Extensive viable tumor at the surgical margins.
- Less than 10% tumor necrosis.
- Large areas of fibrosis and necrosis with minimal viable tumor.
- Presence of multiple skip lesions.
- Intact periosteal reaction with no change in tumor size.
Correct Answer: Large areas of fibrosis and necrosis with minimal viable tumor.
Explanation:
A good response to neoadjuvant chemotherapy is histologically characterized by extensive tumor necrosis (typically >90% necrosis is considered a good response) and replacement of tumor by fibrosis, often with a significant reduction in viable tumor cells. Extensive viable tumor, less than 10% necrosis, or multiple skip lesions would indicate poor response or progression. An intact periosteal reaction with no change in tumor size would suggest lack of response.
Question 43:
The diagnosis of Ewing's Sarcoma often requires a multidisciplinary team approach. Which specialist is primarily responsible for the definitive histological and molecular diagnosis?
Options:
- Orthopedic Surgeon
- Pediatric Oncologist
- Radiation Oncologist
- Pathologist
- Radiologist
Correct Answer: Pathologist
Explanation:
The pathologist is the specialist primarily responsible for the definitive histological diagnosis of Ewing's Sarcoma, often utilizing immunohistochemistry and molecular genetic studies (e.g., FISH for EWSR1 translocations) on biopsy specimens to confirm the diagnosis and differentiate it from other small round blue cell tumors. While all other specialists are crucial in the management, the pathologist makes the tissue diagnosis.
Question 44:
Regarding tumor vascularity in Ewing's Sarcoma, which statement is most accurate?
Options:
- Ewing's Sarcoma is typically avascular, making surgical resection straightforward.
- It is a highly vascular tumor, which can complicate surgical resection and embolization may be considered pre-operatively.
- Tumor vascularity is not a factor in treatment planning.
- It exhibits minimal vascularity, leading to good response to radiation therapy alone.
- Vascularity is only significant in extraskeletal variants.
Correct Answer: It is a highly vascular tumor, which can complicate surgical resection and embolization may be considered pre-operatively.
Explanation:
Ewing's Sarcoma can be a highly vascular tumor, and this vascularity can lead to significant intraoperative bleeding, complicating surgical resection. Pre-operative angiography with embolization of feeding vessels is sometimes considered, particularly for large or difficult-to-access tumors (e.g., pelvic or sacral), to reduce intraoperative blood loss. Tumor vascularity is an important consideration in treatment planning. Avascularity is not typical, and high vascularity does not mean good response to radiation alone.
Question 45:
Which benign condition can mimic the 'onion-skin' periosteal reaction seen in Ewing's Sarcoma on plain radiographs?
Options:
- Osteoid osteoma
- Fibrous dysplasia
- Chronic osteomyelitis
- Non-ossifying fibroma
- Enchondroma
Correct Answer: Chronic osteomyelitis
Explanation:
Chronic osteomyelitis, particularly Brodie's abscess, can produce a lamellated or 'onion-skin' periosteal reaction due to repeated episodes of inflammation and new bone formation, making differentiation from Ewing's Sarcoma challenging. This is why a biopsy is critical when clinical and radiographic features overlap. Osteoid osteoma typically causes a central lucent nidus with dense surrounding sclerosis. Fibrous dysplasia causes a 'ground glass' matrix. Non-ossifying fibroma is a well-defined cortical lesion. Enchondroma is an intramedullary cartilaginous tumor.
Question 46:
For a patient with Ewing's Sarcoma involving a vertebra, what is the primary indication for surgical decompression?
Options:
- Routine procedure for all spinal Ewing's Sarcomas.
- When there is neurological deficit due to spinal cord compression.
- To prevent systemic metastasis.
- To improve the cosmetic outcome of the spine.
- To obtain a definitive diagnosis without prior biopsy.
Correct Answer: When there is neurological deficit due to spinal cord compression.
Explanation:
Surgical decompression for spinal Ewing's Sarcoma is indicated primarily when there is neurological compromise or imminent risk of spinal cord compression, causing deficits such as motor weakness, sensory loss, or bowel/bladder dysfunction. It is an emergent procedure aimed at preserving neurological function, often followed by radiation and chemotherapy. It's not routine for all spinal tumors, does not prevent systemic metastasis, and isn't for cosmetic improvement or initial diagnosis.
Question 47:
Which of the following is an expected complication of Ifosfamide, a common chemotherapy agent used in Ewing's Sarcoma?
Options:
- Cardiotoxicity (dose-dependent)
- Peripheral neuropathy
- Hemorrhagic cystitis
- Ototoxicity
- Pulmonary fibrosis
Correct Answer: Hemorrhagic cystitis
Explanation:
Ifosfamide is an alkylating agent often used in Ewing's Sarcoma. Its most characteristic and serious toxicity is hemorrhagic cystitis, caused by the metabolite acrolein. This is typically prevented by co-administering Mesna (2-mercaptoethane sulfonate sodium). Cardiotoxicity is associated with Doxorubicin. Peripheral neuropathy with Vincristine. Ototoxicity with Cisplatin. Pulmonary fibrosis with Bleomycin or Busulfan (less common in Ewing's regimens).
Question 48:
The concept of 'chemoprimary' management is often applied to Ewing's Sarcoma. What does this refer to?
Options:
- Chemotherapy being the sole treatment modality for all stages of disease.
- Surgical resection being performed before any chemotherapy.
- Chemotherapy is initiated as the first therapeutic step, followed by local control and further chemotherapy.
- Only radiation therapy is used initially, with chemotherapy reserved for recurrence.
- Chemotherapy is administered only after metastasis has been confirmed.
Correct Answer: Chemotherapy is initiated as the first therapeutic step, followed by local control and further chemotherapy.
Explanation:
'Chemoprimary' management signifies that systemic chemotherapy is the initial therapeutic intervention for Ewing's Sarcoma, even before local control (surgery or radiation). This approach aims to treat micrometastatic disease early and reduce the primary tumor burden. Local control (surgery/radiation) follows, and then further systemic chemotherapy is administered. It is not the sole treatment, nor is surgery performed first, and radiation is not typically first line alone.
Question 49:
What is the typical dose range for radiation therapy (external beam) used in the local control of Ewing's Sarcoma?
Options:
- 5-10 Gy
- 20-30 Gy
- 45-60 Gy
- 70-80 Gy
- 100+ Gy
Correct Answer: 45-60 Gy
Explanation:
The typical dose range for external beam radiation therapy in Ewing's Sarcoma is generally between 45-60 Gy (or higher for gross residual disease), delivered in daily fractions over several weeks. This dose is necessary to achieve local tumor control. Doses below 45 Gy are typically insufficient for definitive treatment, while doses above 60 Gy significantly increase the risk of severe long-term complications, particularly in children.
Question 50:
Which tumor marker is sometimes elevated in Ewing's Sarcoma, particularly in patients with larger tumor burdens, and can be used for monitoring, though it is non-specific?
Options:
- Alpha-fetoprotein (AFP)
- Beta-human chorionic gonadotropin (β-hCG)
- Carcinoembryonic antigen (CEA)
- Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP)
- Prostate-specific antigen (PSA)
Correct Answer: Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP)
Explanation:
Erythrocyte Sedimentation Rate (ESR) and C-reactive protein (CRP) are non-specific markers of inflammation that are frequently elevated in Ewing's Sarcoma patients, especially with larger, more aggressive tumors. They can be monitored to assess disease activity and response to treatment, though they are not specific diagnostic markers. AFP and β-hCG are markers for germ cell tumors, CEA for adenocarcinomas, and PSA for prostate cancer.
Question 51:
In a case of Ewing's Sarcoma of the proximal femur in a young adolescent, what surgical challenge is paramount in limb salvage planning?
Options:
- Minimizing blood loss during surgery.
- Avoiding damage to the femoral artery and nerve.
- Maintaining joint function and addressing future limb length discrepancy.
- Ensuring proper callus formation post-operatively.
- Preventing pulmonary embolism.
Correct Answer: Maintaining joint function and addressing future limb length discrepancy.
Explanation:
For Ewing's Sarcoma of the proximal femur in a young adolescent, limb salvage planning faces the paramount challenge of resecting the tumor with adequate margins while maintaining acceptable joint function (e.g., hip joint) and addressing the significant potential for future limb length discrepancy due to removal or radiation of growth plates. While avoiding neurovascular damage and minimizing blood loss are important, the long-term functional and growth implications are especially critical in this age group. Proper callus formation is more relevant for fracture healing or bone graft incorporation. PE is a general surgical risk.
Question 52:
What is the most common site for Ewing's Sarcoma to metastasize to at the time of initial diagnosis?
Options:
- Brain
- Liver
- Lungs
- Kidneys
- Regional lymph nodes
Correct Answer: Lungs
Explanation:
At the time of diagnosis, the lungs are the most common site for distant metastases in Ewing's Sarcoma, observed in approximately 25-30% of patients. Bone and bone marrow are the next most common sites. Brain, liver, and kidneys are less frequent initial metastatic sites. Regional lymph node involvement is less common than in many other solid tumors.
Question 53:
Which molecular technique is most definitive for identifying the specific EWSR1-FLI1 fusion transcript in Ewing's Sarcoma?
Options:
- Western Blot
- Southern Blot
- Reverse Transcription Polymerase Chain Reaction (RT-PCR)
- Karyotyping
- Immunohistochemistry for CD99
Correct Answer: Reverse Transcription Polymerase Chain Reaction (RT-PCR)
Explanation:
Reverse Transcription Polymerase Chain Reaction (RT-PCR) is the most definitive molecular technique for identifying the specific EWSR1-FLI1 fusion transcript by detecting the messenger RNA (mRNA) produced from the fused gene. FISH detects the chromosomal rearrangement, but RT-PCR confirms the functional transcript. Western blot detects protein. Southern blot detects DNA fragments. Karyotyping detects large chromosomal abnormalities but may miss cryptic translocations. Immunohistochemistry for CD99 detects the protein product but is not specific for the fusion transcript.
Question 54:
The main reason for using proton therapy over conventional photon radiation in certain cases of Ewing's Sarcoma is:
Options:
- Proton therapy has a shorter treatment duration.
- Proton therapy causes less acute skin toxicity.
- Proton therapy allows for superior dose conformity, sparing normal tissues and reducing integral dose to the patient.
- Proton therapy is effective for treating metastatic disease.
- Proton therapy is less expensive than photon therapy.
Correct Answer: Proton therapy allows for superior dose conformity, sparing normal tissues and reducing integral dose to the patient.
Explanation:
Proton therapy offers superior dose conformity compared to conventional photon radiation (X-rays). Protons deposit most of their energy at a specific depth (Bragg peak) and then stop, leading to minimal 'exit dose' beyond the target. This property allows for better sparing of surrounding healthy tissues and organs at risk, reducing late toxicities (e.g., secondary malignancies, growth abnormalities, organ damage), which is particularly beneficial for pediatric patients and tumors located near critical structures (e.g., spine, pelvis, skull base). It does not inherently have a shorter duration, cause less acute skin toxicity (though it can reduce chronic toxicity), or treat metastatic disease (it's local therapy). It is generally more expensive.
Question 55:
What is the primary mechanism of action of the EWSR1-FLI1 fusion protein in Ewing's Sarcoma pathogenesis?
Options:
- It acts as a tumor suppressor gene, preventing cell division.
- It promotes DNA repair mechanisms, leading to drug resistance.
- It functions as an aberrant transcription factor, dysregulating gene expression critical for cell proliferation and survival.
- It causes direct degradation of cellular organelles, inducing apoptosis.
- It forms a structural component of the extracellular matrix, stiffening the tumor.
Correct Answer: It functions as an aberrant transcription factor, dysregulating gene expression critical for cell proliferation and survival.
Explanation:
The EWSR1-FLI1 fusion protein acts as an aberrant chimeric transcription factor. The EWSR1 portion contributes a strong transcriptional activation domain, while the FLI1 portion provides DNA binding specificity. This fusion protein then aberrantly activates or represses genes involved in cell growth, differentiation, and survival, driving the oncogenic process. It is not a tumor suppressor, nor does it primarily promote DNA repair, cause organelle degradation, or form extracellular matrix components.
