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10. Pathology and Oncology MCQs

Practice Set 29 of 351

This practice set contains high-yield board review questions covering key concepts in 10. Pathology and Oncology. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 561

Topic: 10. Pathology and Oncology

A 14-year-old male presents with localized pain and swelling in his right femur for several months, accompanied by intermittent fever and weight loss. Radiographs show a lytic lesion in the diaphysis with a characteristic 'onion skin' periosteal reaction. Biopsy reveals small, round, blue cells. Which of the following is the most likely diagnosis?

. Osteosarcoma
. Ewing's sarcoma
. Chondrosarcoma
. Osteoid osteoma
. Fibrous dysplasia

Correct Answer & Explanation

. Ewing's sarcoma

Explanation

Correct Answer: BThe clinical presentation (adolescent, pain, swelling, systemic symptoms like fever and weight loss), radiographic findings (lytic diaphyseal lesion with 'onion skin' periosteal reaction), and histological description (small, round, blue cells) are classic for Ewing's sarcoma. Ewing's sarcoma is a highly malignant bone tumor, often affecting the diaphysis of long bones or flat bones, and is characterized by a specific chromosomal translocation (most commonly t(11;22)). Osteosarcoma (A) typically presents with a 'sunburst' or Codman's triangle appearance and involves the metaphysis. Chondrosarcoma (C) is a cartilage-forming tumor, usually in older adults, with a different radiographic and histological appearance. Osteoid osteoma (D) is a benign tumor characterized by a small lucent nidus and surrounding sclerosis, with pain relieved by NSAIDs. Fibrous dysplasia (E) is a developmental anomaly, not a malignant tumor, and has a 'ground-glass' appearance on radiographs.

Question 562

Topic: 10. Pathology and Oncology

Which of the following clinical findings is *least* typical for a patient presenting with an early, uncomplicated Richter hernia?

. Localized tenderness and a palpable mass at the hernia site
. Significant abdominal distention
. Pain out of proportion to physical findings
. Mild nausea without projectile vomiting
. Ability to pass flatus and stools

Correct Answer & Explanation

. Significant abdominal distention

Explanation

Correct Answer: BSignificant abdominal distention is least typical for an early, uncomplicated Richter hernia because, by definition, only a portion of the bowel wall is entrapped, meaning the bowel lumen is usually not completely obstructed. Patients often present with localized tenderness, a palpable mass (which may be subtle), and pain disproportionate to the seemingly benign findings. They may experience mild nausea but often do not have projectile vomiting and can typically pass flatus and stools, distinguishing it from a complete bowel obstruction. Abdominal distention would suggest a more advanced stage with paralytic ileus secondary to peritonitis or development of a complete obstruction, which is less common initially.

Question 563

Topic: 10. Pathology and Oncology

A 16-year-old female presents with knee pain and swelling. Radiographs reveal a 'sunburst' periosteal reaction in the distal femur. Biopsy confirms high-grade intramedullary osteosarcoma.

Based on the Huvos grading system, what percentage of tumor necrosis following neoadjuvant chemotherapy indicates a favorable prognosis?

. Greater than 50%
. Greater than 75%
. Greater than 80%
. Greater than 90%
. 100% only

Correct Answer & Explanation

. Greater than 90%

Explanation

A favorable histological response to neoadjuvant chemotherapy in osteosarcoma is defined as greater than 90% tumor necrosis. This response rate is one of the most important prognostic factors for long-term survival.

Question 564

Topic: 10. Pathology and Oncology

A 14-year-old boy presents with progressive knee pain and swelling. Radiographs reveal a destructive metaphyseal lesion of the distal femur with a "sunburst" periosteal reaction. Biopsy confirms osteosarcoma. Mutations in which of the following tumor suppressor genes are most strongly associated with the pathogenesis of this tumor?

. BRCA1 and BRCA2
. APC and MUTYH
. RB1 and TP53
. NF1 and NF2
. EXT1 and EXT2

Correct Answer & Explanation

. RB1 and TP53

Explanation

Osteosarcoma is highly associated with mutations in the RB1 (retinoblastoma) and TP53 (Li-Fraumeni syndrome) tumor suppressor genes. Patients with hereditary retinoblastoma have a significantly increased risk of developing osteosarcoma.

Question 565

Topic: 10. Pathology and Oncology

A 9-year-old girl presents with pain and swelling in her diaphyseal femur. Radiographs show a permeative "onion-skin" lesion. A biopsy is sent for molecular testing. Which of the following chromosomal translocations is highly specific for the suspected diagnosis?

. t(11;22)
. t(9;22)
. t(X;18)
. t(12;16)
. t(2;13)

Correct Answer & Explanation

. t(11;22)

Explanation

The clinical presentation and "onion-skin" periosteal reaction are classic for Ewing sarcoma. This tumor is characterized by the t(11;22)(q24;q12) translocation, which creates the EWS-FLI1 fusion protein.

Question 566

Topic: 10. Pathology and Oncology

A 15-year-old boy presents with progressive distal femur pain. Radiographs reveal a sunburst periosteal reaction and a permeative metaphyseal lesion. Biopsy confirms high-grade osteosarcoma. Which of the following represents the most appropriate treatment protocol?

. Wide surgical resection alone
. Neoadjuvant chemotherapy, wide surgical resection, and adjuvant chemotherapy
. Radiation therapy followed by wide surgical resection
. Intralesional curettage, bone grafting, and adjuvant chemotherapy
. Primary amputation without chemotherapy

Correct Answer & Explanation

. Neoadjuvant chemotherapy, wide surgical resection, and adjuvant chemotherapy

Explanation

The standard of care for high-grade osteosarcoma is neoadjuvant chemotherapy, followed by wide surgical resection (often limb salvage), and adjuvant chemotherapy. This multimodal approach significantly improves overall survival and local control.

Question 567

Topic: 10. Pathology and Oncology

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?

. 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 & Explanation

. t(11;22)(q24;q12) EWS-FLI1

Explanation

Correct Answer: AEwing'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 and is the defining molecular hallmark of the Ewing Sarcoma Family of Tumors (ESFT).Incorrect Options:B. t(X;18)(p11.2;q11.2) SYT-SSX1/2:This translocation is characteristic of Synovial Sarcoma.C. t(12;16)(q13;p11) FUS-DDIT3:This translocation is associated with Myxoid Liposarcoma.D. t(2;13)(q35;q14) PAX3-FKHR:This translocation is found in Alveolar Rhabdomyosarcoma.E. t(9;22)(q34;q11) BCR-ABL:This is the Philadelphia chromosome, characteristic of Chronic Myeloid Leukemia (CML).

Question 568

Topic: 10. Pathology and Oncology

A 10-year-old presents with a diaphyseal femur lesion, fever, and elevated ESR. Given the clinical and radiographic findings, which is the most important initial step in differentiating Ewing's Sarcoma from osteomyelitis?

. 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 & Explanation

. Obtain an MRI of the affected limb and a core needle biopsy.

Explanation

Correct Answer: CEwing's Sarcoma can clinically (pain, fever, elevated inflammatory markers like ESR) and radiographically (lytic lesion, periosteal reaction) mimic osteomyelitis, making differentiation crucial. The most important initial step is to perform an MRI to better characterize the lesion's extent, soft tissue component, and relationship to neurovascular structures. This should be followed by a core needle biopsy to obtain tissue for definitive diagnosis, which includes histology, immunohistochemistry (e.g., CD99), and molecular genetics (e.g., FISH for EWSR1 rearrangement). Delaying diagnosis and treatment of Ewing's Sarcoma can have severe consequences.Incorrect Options:A. Start empiric antibiotics for suspected osteomyelitis:While osteomyelitis is in the differential, starting empiric antibiotics without a definitive diagnosis risks delaying appropriate cancer treatment if it is Ewing's Sarcoma.B. Perform an open biopsy immediately:A core needle biopsy is generally preferred as the initial biopsy method for suspected bone tumors, as it is less invasive, allows for appropriate tissue acquisition, and minimizes contamination of tissue planes, which is important for subsequent limb salvage surgery. Open biopsy is reserved for cases where core biopsy is non-diagnostic.D. Monitor symptoms and repeat X-rays in 4-6 weeks:This approach is inappropriate for a potentially aggressive malignancy like Ewing's Sarcoma, which requires urgent diagnosis and treatment.E. Order a white blood cell count and C-reactive protein only:While these are useful inflammatory markers, they are non-specific and cannot differentiate between infection and malignancy. Definitive tissue diagnosis is required.

Question 569

Topic: 10. Pathology and Oncology

A 10-year-old girl is diagnosed with Ewing's Sarcoma of the proximal tibia. Which investigation is crucial for detecting skip lesions and assessing the full intraosseous extent of the tumor in this long bone?

. 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 & Explanation

. MRI of the entire involved bone and adjacent joint

Explanation

Correct Answer: DMagnetic Resonance Imaging (MRI) of the entire involved bone, extending from joint to joint and including the adjacent joints, is the gold standard for local staging of bone and soft tissue tumors like 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 crucially, the detection of 'skip lesions' (discontinuous tumor foci within the same bone). This detailed information is paramount for surgical planning and determining resectability, especially in limb salvage procedures.Incorrect Options:A. Plain X-ray:X-rays are initial screening tools but lack the soft tissue and marrow detail needed to assess the full extent of the tumor or detect skip lesions.B. CT scan of the primary site:CT provides excellent bony detail but is inferior to MRI for evaluating intramedullary extent, soft tissue involvement, and skip lesions.C. Bone scintigraphy (bone scan):Bone scans (Technetium-99m) are highly sensitive for detecting increased metabolic activity in bone, making them useful for screening for skeletal metastases, but they lack the anatomical resolution to precisely define the local tumor extent or skip lesions for surgical planning.E. Ultrasound:Ultrasound is useful for evaluating superficial soft tissue masses and guiding biopsies but has limited utility for assessing intraosseous tumor extent or skip lesions in long bones.

Question 570

Topic: 10. Pathology and Oncology

A biopsy confirms Ewing's Sarcoma. Which of the following describes the typical histological appearance of this tumor?

. 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 & Explanation

. Sheets of small, round, uniform cells with scant cytoplasm, often glycogen-rich

Explanation

Correct Answer: CEwing's Sarcoma is classically described as 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. The nuclei are typically round to oval with fine chromatin and inconspicuous nucleoli. This characteristic appearance, along with positive immunohistochemical staining for CD99 and specific genetic translocations, confirms the diagnosis.Incorrect Options:A. Abundant osteoid production with spindle cells:This is the hallmark histological feature of osteosarcoma.B. Large pleomorphic cells with prominent nucleoli arranged in a herringbone pattern:This description is more typical of a high-grade spindle cell sarcoma, such as an undifferentiated pleomorphic sarcoma or fibrosarcoma.D. Chondroid matrix with entrapped lacunae:This describes a cartilaginous tumor, such as chondrosarcoma or enchondroma.E. Multinucleated giant cells and mononuclear stromal cells:This is the characteristic histological appearance of a Giant Cell Tumor of Bone.

Question 571

Topic: 10. Pathology and Oncology

A 15-year-old male is diagnosed with Ewing's Sarcoma of the proximal humerus. Which of the following is considered the most important negative prognostic factor in this patient?

. 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 & Explanation

. Presence of metastatic disease at diagnosis

Explanation

Correct Answer: DThe 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, even with aggressive multimodal therapy. Common sites of metastasis include the lungs, bone, and bone marrow.Incorrect Options:A. Age greater than 10 years:While very young age (e.g., <5 years) can sometimes be associated with a slightly better prognosis, age greater than 10 years is not considered a primary negative prognostic factor; the peak incidence is in adolescence.B. Tumor size less than 8 cm:Larger tumor size (typically >8 cm or >200 ml) is generally associated with a poorer prognosis, so a tumor size less than 8 cm would be a relatively more favorable factor, not a negative one.C. Primary tumor site in the distal extremity:Distal extremity tumors generally have a more favorable prognosis compared to central axial sites (e.g., pelvis, spine) due to easier resectability and lower rates of local recurrence.E. Elevated LDH:Elevated serum lactate dehydrogenase (LDH) is a non-specific marker that often correlates with higher tumor burden and more aggressive disease, and it is considered a poor prognostic indicator. However, it is secondary to the presence of overt metastatic disease in terms of prognostic impact.

Question 572

Topic: 10. Pathology and Oncology

A 14-year-old patient is diagnosed with an extensive Ewing's Sarcoma of the ilium. The multidisciplinary tumor board recommends neoadjuvant (pre-operative) chemotherapy. What is the primary goal of this initial treatment phase?

. 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 & Explanation

. To reduce tumor size, treat micrometastatic disease, and assess tumor response.

Explanation

Correct Answer: CThe primary goals of neoadjuvant (pre-operative) chemotherapy in Ewing's Sarcoma are multifaceted:Reduce tumor size (debulking):This can make a previously unresectable tumor resectable, facilitate limb-sparing surgery, and improve the chances of achieving wide, tumor-free surgical margins.Treat micrometastatic disease:Ewing's Sarcoma has a high propensity for micrometastasis, and systemic chemotherapy addresses these distant foci early, even if not detectable on initial staging.Assess tumor response:The histological response to neoadjuvant chemotherapy (percentage of tumor necrosis) is a significant prognostic indicator. A good response (typically >90% necrosis) correlates with better outcomes.This 'chemoprimary' approach is standard for Ewing's Sarcoma.Incorrect Options:A. To avoid the need for surgery completely:While chemotherapy can achieve significant tumor regression, it rarely eliminates the need for local control (surgery or radiation) for the primary tumor.B. To improve patient nutrition before surgery:While supportive care is important, improving nutrition is not the primary oncologic goal of neoadjuvant chemotherapy.D. To definitively cure the local tumor without any further treatment:Chemotherapy alone is generally insufficient for definitive local control of the primary tumor; it must be followed by surgery and/or radiation.E. To induce a pathological fracture for easier tumor removal:Inducing a pathological fracture is not a therapeutic goal; it is a complication that can occur due to tumor weakening of the bone and can complicate surgical planning.

Question 573

Topic: 10. Pathology and Oncology

A 16-year-old male with Ewing's Sarcoma of the ilium has completed neoadjuvant chemotherapy. The post-chemotherapy MRI shows significant tumor regression, but surgical margins are anticipated to be close due to the tumor's proximity to the sacroiliac joint and neurovascular structures. What is the primary indication for using radiation therapy in conjunction with surgery in this scenario?

. 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 & Explanation

. To sterilize positive or close surgical margins and treat unresectable disease.

Explanation

Correct Answer: CRadiation 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 (R1 or R2 resection) or close (as anticipated in this pelvic case), or when the tumor is unresectable. In the pelvis, achieving wide, tumor-free margins can be challenging without causing significant morbidity, making adjuvant radiation a common and important strategy to reduce the risk of local recurrence.Incorrect Options:A. As a substitute for systemic chemotherapy:Radiation therapy is a local treatment modality and cannot substitute for systemic chemotherapy, which is essential for treating micrometastatic disease.B. To prevent limb length discrepancy in children:Radiation therapy, especially in growing children, can damage growth plates and actually cause limb length discrepancy and skeletal deformities, rather than preventing them.D. To increase bone density in the treated area:Radiation therapy does not increase bone density; it can lead to osteopenia or osteonecrosis in the long term.E. To induce a pathologic fracture for easier resection:Inducing a pathological fracture is not a therapeutic goal of radiation; it is a potential complication of tumor progression or bone weakening.

Question 574

Topic: 10. Pathology and Oncology

A 13-year-old presents with a painful diaphyseal lesion in the tibia. Radiographs show a lytic lesion with a lamellated ('onion-skin') periosteal reaction and a large soft tissue mass. Which characteristic typically distinguishes Ewing's Sarcoma from osteosarcoma on a plain radiograph?

. 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 & Explanation

. Ewing's often presents with an 'onion-skin' periosteal reaction, while osteosarcoma commonly shows a 'sunburst' or Codman's triangle.

Explanation

Correct Answer: AThe classic radiographic appearance of Ewing's Sarcoma is a lamellated or 'onion-skin' periosteal reaction, which results from layers of reactive bone formation due to the tumor's rapid, infiltrative growth. In contrast, osteosarcoma frequently demonstrates a 'sunburst' periosteal reaction (spicules of bone perpendicular to the cortex) or a Codman's triangle (a triangular elevation of the periosteum at the tumor margin). These distinct periosteal reactions are key differentiating features on plain radiographs.Incorrect Options:B. Ewing's is usually a purely sclerotic lesion, while osteosarcoma is purely lytic:Ewing's Sarcoma is typically a lytic lesion, often with ill-defined margins. Osteosarcoma can be lytic, sclerotic, or mixed (osteoblastic, osteolytic, or chondroblastic).C. Ewing's primarily affects the epiphysis, whereas osteosarcoma affects the diaphysis:Ewing's Sarcoma typically affects the diaphysis or metadiaphysis of long bones and flat bones. Osteosarcoma most commonly affects the metaphysis of long bones. Epiphyseal lesions are more characteristic of chondroblastoma.D. Ewing's lesions typically have sharp, well-defined margins, unlike osteosarcoma:Both Ewing's Sarcoma and osteosarcoma are aggressive malignancies and typically present with ill-defined, permeative margins, indicating their invasive nature.E. Osteosarcoma rarely has a soft tissue mass, while Ewing's always does:Both Ewing's Sarcoma and osteosarcoma frequently present with a significant soft tissue mass, often larger than the intraosseous component, due to cortical breach and extraosseous extension.

Question 575

Topic: 10. Pathology and Oncology

A 14-year-old patient with Ewing's Sarcoma is undergoing chemotherapy, which includes Ifosfamide. The patient develops dysuria and hematuria. Which of the following is an expected complication of Ifosfamide and the most likely cause of these symptoms?

. Cardiotoxicity (dose-dependent)
. Peripheral neuropathy
. Hemorrhagic cystitis
. Ototoxicity
. Pulmonary fibrosis

Correct Answer & Explanation

. Hemorrhagic cystitis

Explanation

Correct Answer: CIfosfamide is an alkylating agent commonly used in the treatment of Ewing's Sarcoma. Its most characteristic and serious toxicity is hemorrhagic cystitis, which is caused by the urotoxic metabolite acrolein. Symptoms include dysuria, frequency, and hematuria. This complication is typically prevented by co-administering Mesna (2-mercaptoethane sulfonate sodium), which inactivates acrolein in the bladder, and ensuring adequate hydration.Incorrect Options:A. Cardiotoxicity (dose-dependent):Cardiotoxicity, particularly dilated cardiomyopathy, is a well-known dose-dependent complication of anthracyclines like Doxorubicin, another agent used in Ewing's regimens, but not primarily Ifosfamide.B. Peripheral neuropathy:Peripheral neuropathy is a common side effect of vinca alkaloids, such as Vincristine, which is also part of Ewing's Sarcoma chemotherapy regimens.D. Ototoxicity:Ototoxicity (hearing loss, tinnitus) is a significant side effect associated with platinum-based agents like Cisplatin, which is not a standard first-line agent for Ewing's Sarcoma.E. Pulmonary fibrosis:Pulmonary fibrosis is a rare but severe complication associated with certain chemotherapy agents like Bleomycin or Busulfan, which are not typically used in standard Ewing's Sarcoma regimens.

Question 576

Topic: 10. Pathology and Oncology
A 55-year-old male presents with a 6 cm, firm, deep-seated mass in his posterior thigh that has been slowly enlarging over the past 8 months. On MRI, the lesion shows predominantly fat signal intensity but also contains several thick (>2mm) enhancing septa and a small, non-fatty nodule. What is the most appropriate next step in management?
. Observation with serial MRI every 6 months
. Immediate wide local excision without prior biopsy
. Fine needle aspiration (FNA) for cytological diagnosis
. Ultrasound-guided core needle biopsy
. Intralesional corticosteroid injection

Correct Answer & Explanation

. Ultrasound-guided core needle biopsy

Explanation

For any suspicious soft tissue mass, especially one that is deep-seated, firm, enlarging, and shows concerning features on MRI (thick enhancing septa, non-fatty nodules), a pre-operative tissue diagnosis is crucial to guide definitive treatment. Ultrasound-guided core needle biopsy is the most appropriate next step. It provides sufficient tissue for histological diagnosis and ancillary studies (e.g., molecular genetics) while minimizing contamination of tissue planes, which is vital for subsequent oncologic resection. Fine needle aspiration (FNA) often yields insufficient tissue for definitive diagnosis and grading of sarcomas. Immediate wide local excision without a biopsy is inappropriate as it risks inadequate margins if the tumor is malignant, or overtreatment if it is benign. Observation is not warranted for a suspicious, enlarging mass. Intralesional injections are not a diagnostic or therapeutic option for suspected sarcomas.

Question 577

Topic: 10. Pathology and Oncology

A 48-year-old patient undergoes MRI for a large retroperitoneal mass. The imaging reveals a predominantly fatty tumor with areas of uniform fat signal intensity, but also a distinct, large, solid, enhancing non-lipomatous component. This combination of findings is highly suggestive of which specific liposarcoma subtype?

. Myxoid liposarcoma
. Pleomorphic liposarcoma
. Well-differentiated liposarcoma (WDLPS)
. Dedifferentiated liposarcoma (DDLPS)
. Lipoma with myxoid degeneration

Correct Answer & Explanation

. Dedifferentiated liposarcoma (DDLPS)

Explanation

Correct Answer: DAcademic Rationale:Dedifferentiated liposarcoma (DDLPS)is characterized by the coexistence of a well-differentiated liposarcoma (WDLPS) component (which appears as a fatty mass on MRI) with a distinct, non-lipogenic, high-grade sarcomatous component (which appears as a solid, enhancing nodule). This bimodal appearance on imaging, with both fatty and solid enhancing components, is highly specific for DDLPS. Myxoid liposarcoma typically presents with a prominent myxoid matrix and a plexiform vascular pattern, while pleomorphic liposarcoma is a high-grade, non-lipogenic sarcoma with pleomorphic cells. Well-differentiated liposarcoma would primarily show fatty signal with potentially thin septa but no distinct solid non-lipomatous nodule. Lipoma with myxoid degeneration is a benign entity and would not exhibit a high-grade solid enhancing component.

Question 578

Topic: Soft Tissue Tumors & Metastasis

A biopsy of a deep soft tissue mass in the thigh reveals a proliferation of primitive round and spindle cells within an abundant myxoid stroma. A delicate plexiform capillary network is noted, and univacuolated lipoblasts are present. These histological features are most characteristic of which liposarcoma subtype?

. Well-differentiated liposarcoma
. Dedifferentiated liposarcoma
. Myxoid liposarcoma
. Pleomorphic liposarcoma
. Spindle cell lipoma

Correct Answer & Explanation

. Myxoid liposarcoma

Explanation

Correct Answer: CAcademic Rationale:The description of a prominent myxoid matrix, a distinctive delicate plexiform capillary network (often described as curvilinear vessels), and a proliferation of small, primitive round and spindle cells, along with the presence of lipoblasts, are the classic histological hallmarks ofmyxoid liposarcoma. Well-differentiated liposarcoma consists primarily of mature adipocytes with atypical stromal cells. Dedifferentiated liposarcoma has a high-grade non-lipogenic component. Pleomorphic liposarcoma is characterized by marked cellular pleomorphism and bizarre giant cells. Spindle cell lipoma is a benign entity with mature adipocytes and uniform spindle cells, lacking the myxoid stroma and plexiform vascularity of myxoid liposarcoma.

Question 579

Topic: 10. Pathology and Oncology

Which of the following genetic translocations is specifically associated with myxoid liposarcoma?

. t(X;18)(p11.2;q11.2) (SYT-SSX fusion)
. MDM2 and CDK4 gene amplification
. FUS-DDIT3 fusion gene (t(12;16))
. EWSR1-FLI1 translocation
. BRAF V600E mutation

Correct Answer & Explanation

. FUS-DDIT3 fusion gene (t(12;16))

Explanation

Correct Answer: CAcademic Rationale:The characteristic genetic alteration found inmyxoid liposarcomais theFUS-DDIT3 fusion gene, resulting from a reciprocal translocation between chromosomes 12 and 16, denoted as t(12;16)(q13;p11). This fusion gene is a key diagnostic marker. The t(X;18) translocation is characteristic of Synovial Sarcoma. MDM2 and CDK4 gene amplification is the hallmark of well-differentiated liposarcoma/atypical lipomatous tumor. EWSR1-FLI1 translocation is associated with Ewing sarcoma. BRAF V600E mutation is seen in melanoma and other cancers, but not typically liposarcoma.

Question 580

Topic: 10. Pathology and Oncology

A 65-year-old patient undergoes wide local excision for a high-grade liposarcoma of the proximal thigh. The pathology report indicates close but negative margins (less than 1 mm). What is the single most significant predictor of local recurrence in this patient?

. Patient's age
. Tumor size
. Histological subtype of liposarcoma
. Margin status of excision
. Adjuvant chemotherapy regimen

Correct Answer & Explanation

. Margin status of excision

Explanation

Correct Answer: DAcademic Rationale:For soft tissue sarcomas, including liposarcomas, themargin status of excisionis consistently the most critical factor influencing local recurrence rates. Achieving negative surgical margins (R0 resection) is paramount for local disease control. While tumor size, histological subtype (especially higher grade), and patient age can influence overall prognosis and risk of recurrence, the adequacy of surgical excision, as reflected by the margin status, is the primary determinant of local control. Close or positive margins significantly increase the risk of local recurrence, often necessitating adjuvant radiotherapy.

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