Orthopedic Oncology Board Review: Soft Tissue Sarcomas

Question 1

A 14-year-old male presents with chronic right knee pain. Radiographs reveal a well-circumscribed, lytic lesion in the proximal tibial epiphysis. A core needle biopsy is performed. Histologic examination demonstrates sheets of mononuclear cells with grooved 'coffee bean' nuclei, scattered multinucleated giant cells, and areas of pericellular 'chicken-wire' calcification. Which of the following is the most appropriate definitive management?

Explanation

The clinical and histologic findings are classic for chondroblastoma, a benign but locally aggressive epiphyseal tumor. The standard of care is extended intralesional curettage using a high-speed burr, often supplemented with chemical adjuvants and bone grafting, to minimize local recurrence.

Question 2

A 32-year-old female presents with a deep, painless, firm mass in her posterior thigh. Biopsy reveals a proliferation of uniform spindle cells in a dense collagenous stroma without cellular atypia or frequent mitoses. Immunohistochemistry is strongly positive for nuclear beta-catenin. In sporadic cases of this specific condition, which of the following genetic alterations is most frequently identified?

Explanation

The diagnosis is extra-abdominal aggressive fibromatosis (desmoid tumor). Sporadic desmoid tumors are primarily driven by mutations in the CTNNB1 gene, which encodes beta-catenin, leading to its abnormal nuclear accumulation.

Question 3

A 55-year-old male is diagnosed with a 10 cm high-grade myxofibrosarcoma of the deep anterior thigh. A multidisciplinary tumor board recommends surgical resection and radiation therapy. Based on randomized clinical trial data comparing preoperative versus postoperative radiation therapy for extremity soft tissue sarcomas, what is the most significant difference between the two approaches?

Explanation

The landmark NCI Canada trial by O'Sullivan et al. demonstrated that preoperative radiation for soft tissue sarcomas results in significantly higher acute wound complication rates compared to postoperative radiation. However, preoperative radiation uses a lower total dose and smaller treatment field, leading to better long-term functional outcomes.

Question 4

A 24-year-old male presents with a slowly enlarging, deep-seated mass near his knee joint. An initial core needle biopsy demonstrates a biphasic tumor with both epithelial and spindle cell components. Which of the following cytogenetic abnormalities is most characteristic of this soft tissue sarcoma?

Explanation

The patient has a synovial sarcoma, which frequently arises near large joints in young adults and can exhibit biphasic (spindle and epithelial) histology. The pathognomonic chromosomal translocation is t(X;18)(p11;q11), resulting in the SYT-SSX fusion gene.

Question 5

A 16-year-old male successfully underwent extended curettage and bone grafting for a proximal humerus chondroblastoma 3 years ago. He now presents for a routine follow-up. While chondroblastoma is classified as a benign primary bone tumor, which of the following rare complications necessitates surveillance imaging in select cases?

Explanation

Chondroblastoma is a benign tumor but is notorious for occasionally producing 'benign' pulmonary metastases. These lung lesions have identical histology to the primary tumor and are typically treated with surgical resection, carrying a much better prognosis than true malignant metastases.

Question 6

A 28-year-old pregnant female notices a slowly enlarging mass in her right abdominal wall. Core biopsy confirms desmoid fibromatosis. The mass is mildly uncomfortable but causes no functional deficit. What is the currently accepted first-line management strategy for this patient?

Explanation

The treatment paradigm for desmoid tumors (fibromatosis) has shifted significantly over the past decade. Due to unpredictable growth patterns, high recurrence rates after surgery, and potential for spontaneous regression, active observation is now the recommended first-line management for asymptomatic or mildly symptomatic lesions.

Question 7

When performing an incisional or core needle biopsy for a suspected extremity soft tissue sarcoma, which of the following technical principles is most critical to avoid compromising the definitive surgical resection?

Explanation

To minimize contamination of normal tissue planes, biopsies of suspected extremity sarcomas must be performed via a longitudinal incision. This allows the entire biopsy tract to be cleanly excised en bloc with the tumor during the definitive wide local excision without creating massive soft tissue defects.

Question 8

A 35-year-old female presents with a 4 cm deep soft tissue mass in her foot. Pathology reveals nests of polygonal cells with clear cytoplasm separated by delicate fibrous septa. Immunohistochemistry is positive for HMB-45 and S-100 protein. Which of the following is the most likely diagnosis?

Explanation

Clear cell sarcoma, also known as melanoma of soft parts, typically arises in the distal extremities of young adults and is characterized by clear polygonal cells. It shares melanocytic differentiation markers (S-100, HMB-45) with cutaneous melanoma but is driven by a distinct t(12;22) translocation.

Question 9

A 17-year-old male presents with shoulder pain. Radiographs reveal an eccentrically located, lytic epiphyseal lesion in the proximal humerus with a thin sclerotic rim. His physes are nearly closed. Based on the typical location and patient age, what is the most likely diagnosis?

Explanation

Chondroblastoma classically presents as a lytic, geographically well-defined lesion in the epiphysis (or apophysis) of a long bone in a skeletally immature or young adult patient. The proximal humerus, distal femur, and proximal tibia are the most common locations.

Question 10

A patient with progressive, unresectable extra-abdominal fibromatosis (desmoid tumor) is enrolled in a clinical trial. They are prescribed Nirogacestat, which recently demonstrated significant efficacy in the DeFi phase 3 trial. What is the mechanism of action of this targeted therapy?

Explanation

Nirogacestat is a novel, selective gamma-secretase inhibitor that blocks the cleavage and activation of the Notch receptor, a pathway heavily implicated in desmoid tumor pathogenesis. It was recently FDA-approved as the first targeted therapy specifically for progressing desmoid tumors.

Question 11

A 62-year-old male presents with a massive, painless mass deep in his thigh. Core needle biopsy demonstrates a lipomatous tumor with fibrous septa and scattered atypical hyperchromatic stromal cells. Which molecular finding is pathognomonic and routinely used to distinguish this well-differentiated liposarcoma from a benign lipoma?

Explanation

Well-differentiated liposarcoma (atypical lipomatous tumor) is characterized by the amplification of the 12q13-15 region, which includes the MDM2 and CDK4 genes. Fluorescence in situ hybridization (FISH) for MDM2 is the gold standard for differentiating it from a benign lipoma.

Question 12

A 23-year-old male presents with a firm, deep-seated nodule in his volar forearm, initially misdiagnosed as a ganglion cyst. Histology shows a nodular growth pattern of epithelioid and spindle cells with central necrosis, mimicking a granuloma. Which immunohistochemical marker is classically LOST in this specific soft tissue sarcoma?

Explanation

The clinical presentation and granuloma-like histology are classic for Epithelioid Sarcoma, a deceptive malignancy often found in the distal upper extremity of young adults. It is characterized by the loss of INI1 (SMARCB1) protein expression on immunohistochemistry due to genetic inactivation.

Question 13

A 68-year-old female undergoes MRI for a slowly growing subcutaneous mass in her distal thigh. The MRI reveals a multinodular superficial mass with a distinct curvilinear 'tail' extending longitudinally along the fascial planes. Biopsy confirms myxofibrosarcoma. Because of this specific imaging and growth characteristic, what clinical challenge is most frequently encountered in the surgical management?

Explanation

Myxofibrosarcoma is notorious for its highly infiltrative growth pattern along fascial planes, classically appearing as a 'tail sign' on MRI. This renders achieving negative surgical margins extremely difficult, leading to a notably high rate of local recurrence compared to other soft tissue sarcomas.

Question 14

A 27-year-old male with a history of recurrent intra-abdominal and extremity soft tissue masses presents for evaluation. Biopsies have consistently shown desmoid fibromatosis. Due to this multifocal presentation, the patient should be urgently screened for mutations in which gene, associated with a potentially fatal gastrointestinal condition?

Explanation

Multifocal desmoid fibromatosis strongly suggests Gardner syndrome, a variant of Familial Adenomatous Polyposis (FAP). FAP is caused by germline mutations in the APC gene and carries a nearly 100% risk of colorectal adenocarcinoma if untreated.

Question 15

While most soft tissue sarcomas metastasize hematogenously to the lungs, a select subset has a higher propensity for lymphatic spread, necessitating routine clinical evaluation of regional lymph nodes. Which of the following sarcomas is included in this distinct subgroup?

Explanation

Soft tissue sarcomas with a high propensity for lymph node metastasis can be remembered by the mnemonic SCARE: Synovial sarcoma, Clear cell sarcoma, Angiosarcoma, Rhabdomyosarcoma, and Epithelioid sarcoma. These require careful regional lymph node evaluation.

Question 16

A patient is undergoing staging for a newly diagnosed high-grade soft tissue sarcoma of the proximal thigh. Which of the following is the most appropriate imaging modality for evaluating the primary tumor for local surgical planning?

Explanation

MRI with and without IV contrast is the gold standard imaging modality for the local evaluation and surgical planning of soft tissue sarcomas. It provides superior soft tissue contrast to delineate tumor extent, neurovascular involvement, and fascial boundaries.

Question 17

In the surgical management of a high-grade soft tissue sarcoma of the extremity without planned adjuvant radiation, what constitutes an 'adequate' oncologic margin to minimize the risk of local recurrence?

Explanation

An adequate wide margin for soft tissue sarcoma resection is defined as a cuff of normal tissue greater than 1 cm in all dimensions, or an intact, uninvolved fascial barrier (such as bone, epimysium, or fascia). Relying on thinner margins requires adjuvant radiation to maintain local control.

Question 18

A 5-year-old child presents with a rapidly enlarging, painless mass in the forearm. A biopsy confirms the most common soft tissue sarcoma of childhood. Histologic subtypes of this tumor carry distinct prognostic implications. The alveolar subtype, which generally has a worse prognosis, is characterized by which specific translocation?

Explanation

The most common soft tissue sarcoma in children is rhabdomyosarcoma. The alveolar subtype is more aggressive than the embryonal subtype and is genetically characterized by the t(2;13)(q35;q14) translocation, producing the PAX3-FOXO1 fusion protein.

Question 19

A 19-year-old female presents with a lytic epiphyseal lesion of the proximal tibia. Biopsy confirms chondroblastoma. The surgeon plans intralesional curettage. Which of the following intraoperative techniques is most strongly associated with a reduced risk of local recurrence for this tumor?

Explanation

For benign but locally aggressive bone tumors like chondroblastoma and giant cell tumor, simple curettage leaves microscopic disease. Extended curettage using a high-speed burr to break the reactive bony rim, often followed by a chemical adjuvant, significantly decreases the local recurrence rate.

Question 20

A 22-year-old female presents with a slow-growing mass in her thigh. Imaging reveals a hypervascular soft tissue mass. Biopsy demonstrates large polygonal cells with prominent nucleoli and an alveolar growth pattern. A diagnostic cytogenetic workup reveals a t(X;17) translocation resulting in an ASPSCR1-TFE3 fusion. Despite a slow local growth rate, what highly characteristic pattern of metastasis requires immediate evaluation?

Explanation

The diagnosis is Alveolar Soft Part Sarcoma (ASPS), characterized by the ASPSCR1-TFE3 fusion. Despite a deceptively slow-growing primary tumor, ASPS has a notorious propensity for early and frequent metastasis to the lungs and brain, mandating brain MRI and chest CT during initial staging.

Question 21

A 15-year-old male presents with knee pain. Radiographs reveal an eccentric, lytic epiphyseal lesion in the proximal tibia. Biopsy shows mononuclear polygonal cells with nuclear grooves and areas of eosinophilic matrix. Which of the following is the hallmark histological pattern of mineralization in this tumor?

Explanation

Chondroblastoma is a benign cartilage tumor characterized histologically by polygonal mononuclear cells (chondroblasts) with grooved 'coffee-bean' nuclei. Fine, pericellular calcifications known as 'chicken-wire' calcifications are pathognomonic.

Question 22

A 15-year-old male presents with chronic knee pain. Radiographs reveal a well-circumscribed, lytic epiphyseal lesion in the distal femur. A biopsy is performed. Histologically, the lesion shows mononuclear cells with longitudinal nuclear grooves and 'chicken-wire' intercellular calcifications. What is the most likely diagnosis?

Explanation

Chondroblastoma typically occurs in the epiphysis of skeletally immature patients. Histology characteristically reveals chondroblasts (mononuclear cells with clefted nuclei) surrounded by fine, lacelike 'chicken-wire' calcifications. Giant cell tumors usually occur after physeal closure.

Question 23

When performing an incisional biopsy for a suspected high-grade soft tissue sarcoma of the anterior thigh, which of the following is an absolute surgical principle?

Explanation

Biopsy incisions for sarcomas must be longitudinal and in line with muscle fibers to allow for en bloc excision of the biopsy tract during definitive wide resection. Transverse incisions contaminate wider tissue planes and complicate definitive limb-sparing surgery. Exsanguination via Esmarch should be avoided to prevent tumor embolization.

Question 24

A 30-year-old female presents with a deep, firm, and fixed mass in her shoulder girdle. Core needle biopsy confirms extra-abdominal aggressive fibromatosis (desmoid tumor). Which genetic alteration is most commonly implicated in the pathogenesis of this tumor?

Explanation

Desmoid tumors (fibromatoses) are strongly associated with mutations in the Wnt/beta-catenin signaling pathway, most commonly a CTNNB1 (beta-catenin) gene mutation in sporadic cases. In familial cases, they are associated with APC gene mutations (Gardner syndrome).

Question 25

A 16-year-old male is diagnosed with an active chondroblastoma of the proximal humerus causing significant joint pain and subchondral erosion. What is the most appropriate initial surgical management?

Explanation

Chondroblastoma is a benign but locally aggressive bone tumor. The standard of care is extended intralesional curettage, often utilizing a high-speed burr and adjuvants (like phenol or liquid nitrogen), followed by packing with bone graft or PMMA cement.

Question 26

A 25-year-old male presents with a slowly growing, painful mass deep within the vastus medialis near the knee joint. Biopsy reveals a biphasic tumor comprised of epithelial and spindle cell components. What is the characteristic cytogenetic abnormality for this diagnosis?

Explanation

The clinical and histologic description represents a synovial sarcoma, which frequently arises near joints (but rarely within them). Its pathognomonic chromosomal translocation is t(X;18), resulting in the SYT-SSX fusion gene.

Question 27

A 28-year-old female is incidentally diagnosed with an asymptomatic 4 cm extra-abdominal desmoid tumor in the posterior thigh musculature. Based on current consensus guidelines, what is the most appropriate initial management strategy?

Explanation

The treatment paradigm for desmoid tumors has shifted significantly away from upfront morbid surgery. The current recommended first-line approach for asymptomatic or minimally symptomatic tumors is active surveillance ('watch and wait'), as many tumors stabilize or spontaneously regress.

Question 28

Which of the following descriptions best outlines the classical radiographic presentation of a chondroblastoma?

Explanation

Chondroblastoma is one of the few bone tumors that characteristically arises in the epiphysis (or apophysis) of long bones in skeletally immature individuals. It presents radiographically as a well-defined, eccentric, lytic lesion often with a thin sclerotic margin.

Question 29

In the surgical management of soft tissue sarcomas, how is a 'wide' surgical margin accurately defined?

Explanation

A wide margin involves excising the tumor completely encompassed within a continuous envelope (cuff) of normal tissue. It does not require removal of the entire anatomical compartment (radical margin), but must avoid breaching the reactive pseudocapsule where satellite cells reside.

Question 30

When multidisciplinary treatment involves radiation for a high-grade extremity soft tissue sarcoma, what is a primary advantage of preoperative radiotherapy compared to postoperative radiotherapy?

Explanation

Preoperative radiotherapy allows for a smaller treatment field and lower total dose (typically 50 Gy) compared to postoperative RT (typically 60-66 Gy), which reduces long-term limb edema and fibrosis. However, it is associated with a significantly higher rate of acute surgical wound complications.

Question 31

A 35-year-old male with a previously observed desmoid tumor of the shoulder girdle now presents with rapid growth, severe pain, and progressive neurologic deficit. Surgical morbidity would be extreme. Which targeted medical therapy is highly effective and increasingly utilized for progressive fibromatosis?

Explanation

For progressive or symptomatic desmoid tumors where surgery would be highly morbid, medical management is preferred. Sorafenib, a tyrosine kinase inhibitor, has shown high efficacy in halting progression and inducing responses in advanced desmoid tumors.

Question 32

A 65-year-old man undergoes resection of a massive, deep intramuscular thigh mass. Pathology demonstrates a dedifferentiated liposarcoma. Which molecular marker is most characteristically amplified in well-differentiated and dedifferentiated liposarcomas?

Explanation

Well-differentiated and dedifferentiated liposarcomas are characterized by supernumerary ring and giant marker chromosomes containing amplification of the 12q13-15 region. This leads to the characteristic over-expression/amplification of MDM2 and CDK4.

Question 33

Although primarily considered a benign bone tumor, chondroblastoma has a known, rare potential to metastasize (so-called 'benign metastasis'). To which organ does it most commonly metastasize?

Explanation

Chondroblastoma can occasionally undergo 'benign metastasis', almost exclusively to the lungs. These pulmonary metastases are histologically identical to the primary benign tumor and can often be cured with surgical wedge resection.

Question 34

In determining the prognosis and risk of distant metastasis for a patient with a newly diagnosed primary extremity soft tissue sarcoma, what is generally considered the single most important prognostic factor?

Explanation

Histologic grade is the most critical prognostic factor for predicting distant metastasis and overall survival in soft tissue sarcomas. While tumor size and depth are also important staging parameters, grade remains the primary determinant of tumor biology.

Question 35

A patient presenting with multiple extra-abdominal and intra-abdominal desmoid tumors should be highly suspected of having, and screened for, which of the following underlying conditions?

Explanation

Multiple desmoid tumors, especially involving the abdomen, are a hallmark of Gardner syndrome, a phenotypic variant of Familial Adenomatous Polyposis (FAP) caused by an APC gene mutation. These patients require colonoscopy to screen for colon cancer.

Question 36

A 22-year-old female is diagnosed with an alveolar soft part sarcoma (ASPS) of the right thigh. Which site of metastasis is uncharacteristically common in this specific sarcoma subtype compared to the general population of soft tissue sarcomas?

Explanation

While the lungs are the most common site of metastasis for almost all soft tissue sarcomas, alveolar soft part sarcoma (ASPS) has an unusually high predilection for brain metastases compared to other soft tissue sarcomas. Staging should routinely include brain imaging.

Question 37

Both chondroblastoma and clear cell chondrosarcoma typically present radiographically as epiphyseal lytic lesions. Which clinical feature best helps differentiate between the two entities prior to definitive biopsy?

Explanation

Age is the critical differentiator. Chondroblastoma occurs almost exclusively in skeletally immature patients (typically ages 10-20), whereas clear cell chondrosarcoma typically presents in adults (ages 20-50) after physeal closure.

Question 38

The vast majority of soft tissue sarcomas metastasize hematogenously to the lungs. However, certain subtypes have a significantly higher propensity for lymphatic spread. Which of the following soft tissue sarcomas belongs to this group?

Explanation

A useful mnemonic for sarcomas that metastasize to lymph nodes is SCARE: Synovial, Clear cell, Angiosarcoma, Rhabdomyosarcoma, and Epithelioid sarcoma. Epithelioid sarcoma often spreads via lymphatics and may present with regional nodal disease.

Question 39

Which magnetic resonance imaging (MRI) feature is highly characteristic of extra-abdominal desmoid tumors, directly reflecting their dense collagenous composition?

Explanation

Desmoid tumors typically exhibit low-signal intensity 'bands' on T2-weighted MRI. These bands correspond histologically to dense, hypocellular collagen bundles interspersed within the more cellular portions of the fibromatosis.

Question 40

A 45-year-old man presents with a deep, painless, 8 cm mass in his anterior thigh. An MRI suggests a soft tissue sarcoma. When planning an incisional biopsy, which of the following is the most critical technical principle?

Explanation

Meticulous hemostasis is critical during sarcoma biopsy to prevent the dissemination of tumor cells via a hematoma. Incisions should be longitudinal, not transverse, and compartmental boundaries must not be violated.

Question 41

A 14-year-old boy presents with knee pain. Radiographs reveal a lytic lesion in the distal femoral epiphysis.

Biopsy is performed. Which histologic feature is diagnostic for this condition?

Explanation

The clinical and radiographic presentation is classic for a chondroblastoma. Histology characteristically shows mononuclear cells with longitudinal nuclear grooves (coffee bean nuclei) and a network of 'chicken-wire' intercellular calcifications.

Question 42

A 32-year-old woman presents with an enlarging, painless mass in her right posteromedial thigh. Core needle biopsy confirms extra-abdominal aggressive fibromatosis (desmoid tumor).

She has no neurovascular deficits. What is the currently recommended initial management?

Explanation

Current consensus favors active surveillance as the first-line management for asymptomatic extra-abdominal desmoid tumors, as many remain stable or spontaneously regress. Surgery is reserved for progressive or highly symptomatic lesions due to high recurrence rates.

Question 43

A 25-year-old male presents with a slow-growing, deep-seated soft tissue mass near the knee joint. Biopsy reveals a biphasic spindle cell and epithelial tumor. Which of the following genetic translocations is pathognomonic for this lesion?

Explanation

Synovial sarcoma classically exhibits the t(X;18) translocation resulting in the SYT-SSX fusion gene. It commonly presents in young adults near joints but rarely involves the intra-articular space.

Question 44

A 14-year-old boy presents with right shoulder pain. Radiographs reveal a well-defined lytic lesion in the proximal humeral epiphysis.

Histology shows mononuclear cells with grooved nuclei and areas of fine, pericellular calcification. Which of the following is the most appropriate definitive management?

Explanation

The clinical and histologic description is classic for chondroblastoma (epiphyseal lesion, coffee-bean nuclei, chicken-wire calcification). The gold standard treatment is extended intralesional curettage with high-speed burring of the walls, followed by bone grafting or cementation.

Question 45

Extra-abdominal aggressive fibromatosis (desmoid tumor) occurs most frequently as a sporadic lesion but can be associated with which of the following inherited syndromes?

Explanation

Aggressive fibromatosis is strongly associated with Gardner syndrome, a variant of Familial Adenomatous Polyposis (FAP) caused by mutations in the APC gene. Sporadic cases typically harbor mutations in the CTNNB1 (beta-catenin) gene.

Question 46

In the multidisciplinary management of high-grade extremity soft tissue sarcomas, a primary advantage of preoperative radiation therapy compared to postoperative radiation therapy is:

Explanation

Preoperative radiation therapy allows for a smaller treatment field and lower total dose compared to postoperative RT, decreasing late complications like joint stiffness and fibrosis. However, it carries a significantly higher risk of acute postoperative wound complications.

Question 47

A 16-year-old female undergoes curettage of a distal femoral chondroblastoma. Two years later, she is found to have two 1-cm asymptomatic pulmonary nodules. Biopsy of a nodule confirms chondroblastoma. What is the most appropriate management?

Explanation

Chondroblastoma is a benign tumor that occasionally metastasizes to the lungs (benign pulmonary implants). These implants are typically non-progressive or slow-growing, and surgical resection is the treatment of choice, carrying an excellent long-term prognosis.

Question 48

A 35-year-old female presents with a painless, palpable mass in her posterior thigh.

Core needle biopsy reveals bland, uniform spindle cells arranged in sweeping fascicles with abundant collagen and no nuclear atypia. Which of the following represents the most currently accepted initial management strategy for this asymptomatic lesion?

Explanation

Extra-abdominal aggressive fibromatosis (desmoid tumors) often have an unpredictable course, including spontaneous regression. Current consensus guidelines recommend an initial period of active surveillance for asymptomatic tumors before initiating medical therapy or surgery.

Question 49

When performing an incisional biopsy of a suspected soft tissue sarcoma in the extremity, which of the following technical principles MUST be strictly adhered to?

Explanation

Biopsy incisions for suspected sarcomas must be longitudinal and placed in-line with the planned definitive surgical incision so the entire tract can be excised en bloc. Transverse incisions contaminate wider tissue planes and complicate definitive wide excision.

Question 50

A 65-year-old man presents with a large, deep intramuscular thigh mass.

Molecular testing of the biopsy specimen demonstrates amplification of the MDM2 and CDK4 genes. What is the most likely diagnosis?

Explanation

Well-differentiated liposarcoma (atypical lipomatous tumor) and dedifferentiated liposarcoma are characterized by the amplification of MDM2 and CDK4 on chromosome 12. This distinguishes them from benign lipomas, which lack this amplification.

Question 51

Which of the following secondary lesions is most frequently associated with a chondroblastoma?

Explanation

Approximately 15% to 20% of chondroblastomas are associated with a secondary aneurysmal bone cyst (ABC). Recognition of both components is critical to ensure thorough curettage and minimize the risk of recurrence.

Question 52

According to current orthopedic oncology principles, what defines a "wide" surgical margin for a high-grade soft tissue sarcoma?

Explanation

A wide margin involves removing the tumor completely enclosed within a continuous cuff of normal surrounding tissue. Intralesional and marginal excisions leave macroscopic or microscopic disease, respectively, while a radical margin involves removing the entire compartment.

Question 53

A patient with recurrent, progressive extra-abdominal fibromatosis (desmoid tumor) has failed initial active surveillance. Based on recent clinical trials, which of the following oral targeted therapies is considered a first-line medical treatment?

Explanation

Sorafenib, a multi-kinase inhibitor, has demonstrated significant progression-free survival benefits in patients with progressive, unresectable desmoid tumors. Other active targeted agents include gamma-secretase inhibitors like nirogacestat.

Question 54

While chondroblastoma typically occurs in the epiphyses of long bones, which of the following is the most common location in the foot?

Explanation

In the foot, chondroblastomas most commonly arise in the talus and calcaneus. These tarsal bones develop from secondary ossification centers and are considered apophyseal equivalents, which aligns with the tumor's affinity for epiphyseal/apophyseal cartilage.

Question 55

A 45-year-old male is diagnosed with an extremity soft tissue sarcoma. Staging imaging must routinely include the chest because the lungs are the most common site of metastasis. Which of the following soft tissue sarcomas requires additional whole-spine MRI screening due to its propensity for extrapulmonary bone metastases?

Explanation

Myxoid liposarcoma is unique among soft tissue sarcomas for its high propensity to metastasize to extrapulmonary sites, particularly the spine and other bones. Therefore, staging protocols for this tumor must include cross-sectional imaging (MRI) of the whole spine.

Question 56

A biopsy of a soft tissue tumor demonstrates the t(12;16) translocation resulting in a FUS-DDIT3 fusion protein. Which of the following histologic features is classically associated with this tumor?

Explanation

The t(12;16) translocation and FUS-DDIT3 fusion are diagnostic for myxoid liposarcoma. Histologically, it is characterized by a prominent myxoid stroma, a rich plexiform (chicken-wire) capillary network, and varying numbers of lipoblasts.

Question 57

During the curettage of a proximal tibial chondroblastoma in a 13-year-old with open physes, the surgeon must balance thorough tumor removal with physeal preservation. Which of the following adjuvants carries the HIGHEST risk of irreversible physeal damage if applied directly to the physeal border?

Explanation

Liquid nitrogen (cryotherapy) causes severe, deep tissue necrosis and has a very high risk of destroying the adjacent open physis, leading to premature closure and growth arrest. Chemical adjuvants and burring are generally more controllable near the growth plate.

Question 58

Which of the following soft tissue sarcomas is most notorious for spreading via the lymphatic system, thereby necessitating clinical or radiographic evaluation of the regional lymph nodes?

Explanation

Sarcomas that commonly metastasize to lymph nodes can be remembered by the mnemonic SCARE: Synovial, Clear cell, Angiosarcoma, Rhabdomyosarcoma, and Epithelioid sarcoma. Epithelioid sarcoma has one of the highest rates of lymphatic spread.

Question 59

A patient presents with an aggressive fibromatosis (desmoid tumor) in the shoulder girdle. Immunohistochemistry of the biopsy specimen will most consistently demonstrate strong nuclear staining for which of the following proteins?

Explanation

Aberrant nuclear localization of beta-catenin is the hallmark immunohistochemical feature of desmoid tumors. This is driven by mutations in either the CTNNB1 gene or the APC gene, which prevent the normal degradation of beta-catenin.

Question 60

A 16-year-old male presents with chronic right shoulder pain. Radiographs reveal an eccentric, lytic lesion in the proximal humeral epiphysis with a thin sclerotic rim.

Biopsy confirms a benign cartilaginous tumor. What is the most common cytogenetic abnormality associated with this specific lesion?

Explanation

Chondroblastoma characteristically harbors an H3F3A or H3F3B K36M mutation. Giant cell tumors of bone, which can also appear in the epiphysis, typically exhibit an H3F3A G34W mutation.

Question 61

A 24-year-old male presents with a slow-growing, painful mass near his knee joint. MRI shows a well-defined mass adjacent to the joint capsule, and biopsy confirms a biphasic tumor with both epithelial and spindle cell components. Which chromosomal translocation is diagnostic for this tumor?

Explanation

Synovial sarcoma is uniquely characterized by the t(X;18)(p11;q11) translocation, which creates the SYT-SSX fusion gene. It often presents in young adults near large joints and can exhibit biphasic or monophasic histology.

Question 62

A 28-year-old postpartum female presents with a slowly enlarging, mildly symptomatic mass in her anterior abdominal wall. Core biopsy confirms extra-abdominal fibromatosis.

According to current treatment guidelines, what is the most appropriate initial management?

Explanation

Active observation (a "wait-and-see" approach) is now the recommended first-line management for asymptomatic or mildly symptomatic desmoid tumors. Spontaneous regression is observed in up to 20-30% of cases, particularly those associated with pregnancy.

Question 63

A 45-year-old male presents with a large, deep thigh mass. Biopsy reveals a myxoid background, a plexiform "chicken-wire" capillary network, and lipoblasts. Which genetic translocation is characteristically present in this malignancy?

Explanation

Myxoid liposarcoma is characterized by the t(12;16)(q13;p11) translocation, resulting in the FUS-DDIT3 fusion. Unlike other soft tissue sarcomas, it has a unique propensity to metastasize to extrapulmonary sites like the spine and other soft tissues.

Question 64

A 60-year-old male is scheduled for a wide resection of an undifferentiated pleomorphic sarcoma in his proximal thigh.

In randomized trials comparing preoperative versus postoperative radiation therapy for soft tissue sarcomas, postoperative radiation is associated with a significantly higher risk of which complication?

Explanation

Postoperative radiation requires a higher total dose and larger treatment volume compared to preoperative radiation. This leads to significantly higher rates of long-term morbidities such as tissue fibrosis, joint stiffness, and chronic edema.

Question 65

A 17-year-old female presents with a biopsy-proven chondroblastoma of the proximal tibial epiphysis. She is treated with intralesional curettage and bone grafting. Which of the following is true regarding the systemic behavior of this tumor?

Explanation

Although chondroblastoma is a benign tumor, it can rarely produce "benign" pulmonary metastases (1-2% of cases). These lung lesions typically have limited growth potential and are treated successfully with wedge resection.

Question 66

A 35-year-old male presents with a large, progressive desmoid tumor of the shoulder girdle.

He reports a strong family history of colon cancer and osteomas. He is most likely to harbor a germline mutation in which gene?

Explanation

Desmoid tumors are strongly associated with Familial Adenomatous Polyposis (Gardner syndrome), caused by germline mutations in the APC gene. Sporadic desmoid tumors, however, are usually driven by somatic mutations in the CTNNB1 (beta-catenin) gene.

Question 67

A 30-year-old female presents with a deep mass intimately associated with the Achilles tendon. Biopsy reveals nests of pale, spindle-shaped cells that stain strongly positive for HMB-45 and S-100. The tumor exhibits a t(12;22) translocation. What is the diagnosis?

Explanation

Clear cell sarcoma (historically called melanoma of soft parts) typically arises near tendons or aponeuroses in young adults. It is positive for melanocytic markers (S-100, HMB-45) and is characterized by the EWSR1-ATF1 t(12;22) fusion.

Question 68

Which histological feature is considered classic for chondroblastoma when examining tissue from an epiphyseal lytic lesion in an adolescent?

Explanation

Chondroblastoma is classically characterized by polygonal mononuclear cells with grooved "coffee bean" nuclei and a fine network of pericellular "chicken-wire" calcifications. Osteoclast-like giant cells are also frequently interspersed.

Question 69

A 25-year-old male presents with a firm, slow-growing, ulcerating nodule on his right index finger, initially misdiagnosed as a wart. Biopsy reveals a nodular proliferation of epithelioid cells with central necrosis. Which statement regarding the metastatic behavior of this specific sarcoma is correct?

Explanation

Epithelioid sarcoma commonly presents as a superficial ulcerating nodule on the distal extremities of young adults. Uniquely among soft tissue sarcomas, it has a very high rate of regional lymph node metastasis, necessitating nodal evaluation.

Question 70

A 33-year-old female presents with an unresectable, highly symptomatic extra-abdominal desmoid tumor involving the neurovascular bundle of her lower extremity.

Which systemic targeted therapy has been recently FDA-approved specifically for progressive, unresectable desmoid tumors?

Explanation

Nirogacestat, an oral gamma-secretase inhibitor, is the first FDA-approved systemic therapy for progressing desmoid tumors. It acts by preventing the cleavage of Notch, disrupting the pathway crosstalk that drives these tumors.

Question 71

According to the AJCC staging system for soft tissue sarcomas of the extremities, which of the following is the most critical prognostic factor for predicting the risk of distant metastasis and determining the overall stage?

Explanation

Histologic grade (typically assessed by the FNCLCC grading system) is the single most important prognostic factor for soft tissue sarcomas. It heavily dictates the risk of distant metastasis and overall survival.

Question 72

A 5-year-old boy presents with a rapidly enlarging, deep mass in his forearm. Biopsy confirms alveolar rhabdomyosarcoma. What cytogenetic abnormality is most frequently associated with this diagnosis?

Explanation

Alveolar rhabdomyosarcoma is characterized by the t(2;13)(q35;q14) translocation, generating the PAX3-FOXO1 fusion protein. This subtype generally carries a worse prognosis compared to embryonal rhabdomyosarcoma.

Question 73

A 65-year-old female presents with a large mass in her posterior thigh. Core needle biopsy demonstrates a well-differentiated liposarcoma (atypical lipomatous tumor).

Which molecular marker amplification is diagnostic for this entity?

Explanation

Well-differentiated liposarcomas and dedifferentiated liposarcomas are characterized by the amplification of MDM2 and CDK4 genes on chromosome 12q13-15. MDM2 acts to inhibit the p53 tumor suppressor pathway.

Question 74

When planning surgical resection of a high-grade, undifferentiated pleomorphic sarcoma of the thigh, which of the following constitutes an adequate "wide" surgical margin?

Explanation

A "wide" surgical margin requires removing the tumor completely intact along with a continuous surrounding cuff of normal, healthy tissue. The pseudocapsule and reactive zone often contain microscopic satellite tumor cells and must be resected.

Question 75

A 16-year-old male presents with right knee pain. Radiographs show a lytic, well-circumscribed lesion in the proximal tibial epiphysis. MRI demonstrates fluid-fluid levels within the lesion.

Biopsy confirms sheets of mononuclear cells with grooved nuclei. Which of the following is the most likely diagnosis?

Explanation

Chondroblastoma typically presents as an epiphyseal lytic lesion in young patients. Secondary aneurysmal bone cysts (ABCs), characterized by fluid-fluid levels on MRI, occur in up to 20-30% of chondroblastomas.

Question 76

A 35-year-old female presents with a slowly enlarging, painless mass in the deep tissues of her posterior thigh. Core needle biopsy reveals extra-abdominal fibromatosis. Which of the following is the currently recommended first-line management for an asymptomatic lesion in this location?

Explanation

Active observation is the first-line management for asymptomatic, non-life-threatening extra-abdominal fibromatosis (desmoid tumors). Many of these tumors exhibit prolonged periods of stability or even spontaneous regression.

Question 77

A 24-year-old male presents with a deep, slow-growing mass in his foot. Radiographs show stippled calcifications within the soft tissue mass. Biopsy reveals a biphasic pattern of spindle and epithelial cells. Which of the following chromosomal translocations is diagnostic?

Explanation

Synovial sarcoma classically presents in the distal extremities of young adults and may contain calcifications in up to 30% of cases. It is driven by the t(X;18) translocation resulting in the SYT-SSX fusion gene.

Question 78

A 45-year-old male is diagnosed with a 12 cm deep myxoid liposarcoma of the thigh. As part of his systemic staging workup, which of the following imaging modalities is uniquely indicated for this specific histologic subtype?

Explanation

Myxoid liposarcoma has a unique propensity to metastasize to extrapulmonary locations, particularly the spine and other bones. Total spine MRI is standard in the staging workup for this specific subtype.

Question 79

A 28-year-old female presents with a firm mass in her abdominal wall. She has a family history of Gardner syndrome. Her biopsy confirms a desmoid tumor. Germline mutation in which of the following genes is most likely responsible for her condition?

Explanation

Gardner syndrome is a phenotypic variant of Familial Adenomatous Polyposis (FAP) caused by germline mutations in the APC gene. It strongly predisposes patients to developing desmoid fibromatosis.

Question 80

A 21-year-old male develops a multi-lobulated, ulcerating mass on the palmar aspect of his right hand. Examination reveals palpable axillary lymphadenopathy. Histologic analysis shows epithelioid cells with a loss of SMARCB1 (INI1) expression. What is the most likely diagnosis?

Explanation

Epithelioid sarcoma typically presents in the distal extremities (hand/wrist) of young adults, often ulcerates mimicking a benign process, and has a high rate of lymphatic spread. Loss of INI1 is a characteristic immunohistochemical finding.

Question 81

A 19-year-old male underwent extended curettage and bone grafting for a proximal humerus chondroblastoma 2 years ago. He now presents with a routine surveillance chest CT showing multiple small, well-circumscribed, calcified lung nodules. He is asymptomatic. What is the most appropriate management of the pulmonary findings?

Explanation

Chondroblastoma is a benign tumor that can rarely metastasize to the lungs (benign pulmonary implants). These implants are often slow-growing or non-progressive, and asymptomatic lesions can typically be observed.

Question 82

A 68-year-old male presents with a rapidly growing, painless mass in the superficial subcutaneous tissues of his thigh. MRI reveals a lobulated mass with a characteristic "tail-like" extension along the fascial planes. What is the most likely histologic diagnosis?

Explanation

Myxofibrosarcoma commonly presents as a superficial mass in elderly patients. Its classic MRI feature is a 'fascial tail' representing infiltrative tumor spread, which contributes to a high rate of local recurrence if margins are inadequate.

Question 83

A 30-year-old female presents with an enlarging mass deep to the Achilles tendon.

Biopsy demonstrates nests of uniform spindle cells that stain strongly positive for S-100 and HMB-45. Which of the following translocations is associated with this tumor?

Explanation

Clear cell sarcoma (melanoma of soft parts) typically arises in association with tendons and aponeuroses of the foot and ankle. It is characterized by t(12;22) resulting in the EWSR1-ATF1 fusion and stains positive for melanocytic markers.

Question 84

A 40-year-old male undergoes a core needle biopsy for a suspected soft tissue sarcoma in the anterior compartment of the thigh. To minimize the risk of tumor seeding and optimize definitive oncologic resection, which of the following biopsy techniques is strictly required?

Explanation

Biopsy tracts for suspected sarcomas must be placed longitudinally and directly within the planned surgical excision tract to allow en bloc removal of the biopsy tract during definitive wide resection.

Question 85

Molecular analysis of a typical epiphyseal chondroblastoma from a 14-year-old patient is most likely to reveal a somatic mutation in which of the following histone genes?

Explanation

Over 90% of chondroblastomas harbor a highly specific H3F3B K36M mutation. In contrast, the H3F3A G34W mutation is characteristic of giant cell tumor of bone.

Question 86

A 32-year-old female presents with a progressively enlarging, painful desmoid tumor of the shoulder girdle that is not amenable to function-preserving surgery. She has failed initial observation. What novel, FDA-approved gamma-secretase inhibitor represents a targeted systemic treatment option for this patient?

Explanation

Nirogacestat is an oral gamma-secretase inhibitor recently FDA-approved specifically for progressing desmoid tumors (aggressive fibromatosis) in adults. It works by blocking Notch signaling.

Question 87

A 23-year-old female presents with a highly vascular, slow-growing mass in her right gluteal region. Staging imaging unexpectedly reveals multiple pulmonary nodules and a solitary brain metastasis. Biopsy of the primary tumor shows large cells with eosinophilic granular cytoplasm arranged in a pseudoalveolar pattern. What is the most likely diagnosis?

Explanation

Alveolar soft part sarcoma often presents insidiously as a highly vascular mass in young adults. It is notorious for presenting with advanced disease, frequently metastasizing to the lungs and brain.

Question 88

Which of the following soft tissue sarcomas has the highest propensity for regional lymph node metastasis?

Explanation

The sarcomas most likely to metastasize to lymph nodes can be remembered by the mnemonic SCARE: Synovial, Clear cell, Angiosarcoma, Rhabdomyosarcoma, and Epithelioid sarcoma.

Question 89

A 65-year-old female presents with an enlarging, hard mass in her right axilla and chest wall. She underwent a lumpectomy and local radiation therapy for breast cancer 12 years ago. Core biopsy reveals a high-grade spindle cell proliferation with marked pleomorphism. What is the most common histologic subtype of post-radiation sarcoma in this setting?

Explanation

Post-radiation sarcomas typically arise in the radiation field after a latency of at least 3-5 years (often 10+). Undifferentiated pleomorphic sarcoma (UPS) and angiosarcoma are the most common histologic subtypes.

Question 90

A patient with a high-grade soft tissue sarcoma of the extremity is deciding between preoperative and postoperative radiation therapy. According to randomized clinical trials (e.g., O'Sullivan et al.), what complication is significantly more common with postoperative radiation therapy compared to preoperative radiation?

Explanation

Postoperative radiation utilizes higher total doses and larger fields, leading to greater long-term tissue fibrosis, joint stiffness, and edema. Preoperative radiation has a higher risk of acute wound healing complications.

Question 91

A 16-year-old male presents with heel pain. Imaging reveals a well-defined lytic lesion in the posterior calcaneus. Histology confirms chondroblastoma. Why does chondroblastoma occur in this specific location despite not being a long bone epiphysis?

Explanation

Chondroblastomas almost exclusively arise in secondary centers of ossification. In the foot, the calcaneal apophysis (where the Achilles tendon inserts) acts as an epiphyseal equivalent, making it a classic location.

Question 92

When evaluating the necessity of surgical margins for the treatment of extra-abdominal desmoid fibromatosis, current evidence indicates that:

Explanation

Recent studies show that local recurrence rates for desmoid tumors are similar whether margins are negative (R0) or microscopically positive (R1). Therefore, aggressive, morbid surgeries to achieve wide margins are discouraged.

Question 93

A 72-year-old female presents with chronic, severe lymphedema of her left arm secondary to radical mastectomy and axillary node dissection 15 years prior. She recently developed multiple raised, purplish, ulcerating nodules on the affected arm. What is the most likely diagnosis?

Explanation

Stewart-Treves syndrome refers to the development of an angiosarcoma in the setting of chronic lymphedema, classically following axillary lymph node dissection for breast cancer.

Question 94

In adult soft tissue sarcomas of the extremities, which of the following is considered the single most important prognostic factor for distant metastasis and overall survival?

Explanation

Histologic grade is the most critical independent prognostic factor for distant metastasis and overall survival in adult soft tissue sarcomas. High-grade tumors have a significantly higher risk of systemic spread.

Question 95

A 34-year-old female presents with progressive pain and a slowly enlarging mass in the deep posterior thigh. MRI reveals an infiltrative, poorly marginated soft tissue mass encasing the sciatic nerve.

A core needle biopsy is performed, and histologic examination demonstrates a uniform proliferation of spindle cells lacking atypia in a dense collagenous stroma. Active observation is initially selected, but 6 months later, serial MRI shows 30% enlargement of the mass and the patient reports worsening neuropathic pain. Given the anticipated high functional morbidity of surgical resection, systemic medical therapy is planned. Based on phase III randomized trial data, which of the following agents is most appropriate to improve progression-free survival in this specific condition?

Explanation

Extra-abdominal fibromatosis (desmoid tumor) is a locally aggressive, non-metastasizing neoplasm where active observation is the initial standard of care. For progressive, symptomatic tumors where surgery carries high morbidity, tyrosine kinase inhibitors like sorafenib (or specific gamma-secretase inhibitors like nirogacestat) have been shown to significantly improve progression-free survival. Imatinib is typically indicated for dermatofibrosarcoma protuberans (DFSP), while denosumab is used for giant cell tumor of bone.

Orthopaedic Surgery Board Exam Review: ABOS Part I & AAOS OITE Prep Questions | Part 22210

Orthopedic Oncology Board Review: Soft Tissue Sarcomas, Chondroblastoma & Fibromatosis | Part 17

Key Takeaway

Orthopedic Oncology Board Review: Soft Tissue Sarcomas, Chondroblastoma & Fibromatosis | Part 17

Chapter Index