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10. Pathology and Oncology MCQs

Practice Set 348 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 6941

Topic: Bone Tumors

A 14-year-old boy presents with a painless limp. Pelvic radiographs display a well-defined, radiolucent lesion with a ground-glass appearance in the proximal femur, causing a shepherd's crook varus deformity. A somatic activating mutation in which of the following genes is responsible for this lesion?

. EXT1
. GNAS
. COMP
. FGFR3
. SOX9

Correct Answer & Explanation

. GNAS

Explanation

Fibrous dysplasia is caused by a sporadic, somatic activating mutation in the GNAS gene. This leads to increased intracellular cAMP, causing abnormal proliferation and differentiation of osteoblasts.

Question 6942

Topic: Bone Tumors

A 5-year-old boy presents with a painless, progressively enlarging swelling on the medial aspect of his right ankle. Radiographs demonstrate an asymmetric, irregular mass of ossifying cartilage arising from the medial epiphysis of the distal tibia. What is the most likely diagnosis?

. Multiple epiphyseal dysplasia
. Dysplasia epiphysealis hemimelica (Trevor disease)
. Chondroblastoma
. Enchondromatosis (Ollier disease)
. Osteochondroma

Correct Answer & Explanation

. Dysplasia epiphysealis hemimelica (Trevor disease)

Explanation

Dysplasia epiphysealis hemimelica (Trevor disease) is a rare developmental disorder characterized by an asymmetrical, osteochondroma-like overgrowth of cartilage in an epiphysis, most commonly affecting the medial side of the ankle or knee.

Question 6943

Topic: Bone Tumors

A 4-year-old boy presents with an asymmetric, painless swelling on the medial aspect of his left ankle. Radiographs reveal irregular ossification centers arising from the medial epiphysis of the distal tibia, resembling an intra-articular osteochondroma. What is the most likely diagnosis?

. Dysplasia epiphysealis hemimelica
. Multiple hereditary exostoses
. Fibrodysplasia ossificans progressiva
. Melorheostosis
. Chondrodysplasia punctata

Correct Answer & Explanation

. Dysplasia epiphysealis hemimelica

Explanation

Dysplasia epiphysealis hemimelica (Trevor disease) is a localized developmental abnormality characterized by asymmetric osteochondral overgrowth of an epiphysis. It most commonly affects the medial side of the lower extremity joints, particularly the ankle or knee.

Question 6944

Topic: Bone Tumors

A 5-year-old boy presents with a painless, asymmetric swelling over the medial aspect of his right ankle. Radiographs demonstrate an irregular, multicentric ossification center arising from the medial epiphysis of the distal tibia. What is the most appropriate initial management for this condition?

. Immediate wide excision
. Observation if asymptomatic
. Below-knee amputation
. Administration of bisphosphonates
. Curettage and bone grafting

Correct Answer & Explanation

. Observation if asymptomatic

Explanation

Dysplasia epiphysealis hemimelica (Trevor disease) is a rare focal skeletal dysplasia presenting as asymmetrical epiphyseal overgrowth, pathologically identical to an osteochondroma. Asymptomatic lesions are observed, while surgery is reserved for pain, progressive deformity, or mechanical mechanical restriction.

Question 6945

Topic: 10. Pathology and Oncology

Regarding the management of the lesion described in the previous question (Chondromyxoid Fibroma), which of the following represents the standard of care with the lowest recurrence rate while preserving joint function?

. Observation with serial radiographs
. Simple intralesional curettage
. Extended intralesional curettage with high-speed burring and bone grafting or cementation
. Wide en bloc resection and endoprosthetic reconstruction
. Neoadjuvant chemotherapy followed by curettage

Correct Answer & Explanation

. Extended intralesional curettage with high-speed burring and bone grafting or cementation

Explanation

CMF is a benign but locally aggressive tumor. Extended intralesional curettage (using a high-speed burr and/or phenol) followed by bone grafting or PMMA cementation is the standard treatment, yielding low recurrence rates.

Question 6946

Topic: 10. Pathology and Oncology

A 65-year-old male complains of progressive thigh pain. Radiographs demonstrate a large, permeative, moth-eaten osteolytic lesion in the femoral diaphysis with minimal periosteal reaction.

Biopsy reveals sheets of large atypical cells. Which immunohistochemical marker profile confirms the most common histological subtype of this disease?

. CD99 positive, FLI-1 positive, LCA negative
. CD20 positive, CD45 positive, CD3 negative
. Cytokeratin positive, EMA positive, S100 negative
. CD68 positive, S100 positive, CD1a positive
. CD138 positive, Kappa/Lambda restricted, CD20 negative

Correct Answer & Explanation

. CD20 positive, CD45 positive, CD3 negative

Explanation

Primary bone lymphoma is most commonly Diffuse Large B-Cell Lymphoma (DLBCL). The tumor cells will be positive for B-cell markers (CD20) and leukocyte common antigen (CD45), but negative for T-cell markers (CD3).

Question 6947

Topic: 10. Pathology and Oncology

Which of the following demographic and radiographic features best distinguishes Chondromyxoid Fibroma (CMF) from Chondroblastoma?

. CMF typically occurs in the 5th decade, while chondroblastoma occurs in adolescents
. CMF is primarily located in the epiphysis, while chondroblastoma is diaphyseal
. CMF is usually located in the metaphysis, whereas chondroblastoma is classically epiphyseal
. CMF is characterized by heavy central calcifications, which are absent in chondroblastoma
. CMF presents with a prominent sunburst periosteal reaction, unlike chondroblastoma

Correct Answer & Explanation

. CMF is usually located in the metaphysis, whereas chondroblastoma is classically epiphyseal

Explanation

While both are benign cartilage tumors of young adults, CMF typically arises in the metaphysis (often eccentrically), whereas chondroblastoma almost exclusively arises in the epiphysis or apophysis.

Question 6948

Topic: 10. Pathology and Oncology

When evaluating a bone biopsy for a suspected primary bone lymphoma, what morphological and immunohistochemical characteristic most reliably excludes Ewing sarcoma?

. Presence of uniform small round blue cells
. Positivity for CD99
. Positivity for CD45 (Leukocyte Common Antigen)
. Negative staining for PAS (Periodic acid-Schiff)
. Presence of a high nuclear-to-cytoplasmic ratio

Correct Answer & Explanation

. Positivity for CD45 (Leukocyte Common Antigen)

Explanation

Primary bone lymphoma (typically Diffuse Large B-cell Lymphoma) strongly expresses CD45 (LCA), which distinguishes it from Ewing sarcoma. Both can sometimes stain positive for CD99, making LCA a critical differentiating marker.

Question 6949

Topic: 10. Pathology and Oncology

A pathologist is reviewing a biopsy of an eccentric, lytic proximal tibial lesion. To confidently differentiate Chondromyxoid Fibroma (CMF) from a low-grade Chondrosarcoma, which key histological feature of CMF should be identified?

. Hypercellularity at the periphery of the lobules
. Hypercellularity at the center of the lobules
. Abundant host bone entrapment
. Extensive permeation of the Haversian canals
. Lack of any myxoid or fibrous stroma

Correct Answer & Explanation

. Hypercellularity at the periphery of the lobules

Explanation

A defining histologic feature of Chondromyxoid Fibroma is its lobular pattern with distinct hypercellularity at the periphery of the lobules. In contrast, chondrosarcomas typically show central hypercellularity within the lobules and invasive permeation of host bone.

Question 6950

Topic: 10. Pathology and Oncology

Which of the following demographic profiles best represents the peak incidence for the development of Chondromyxoid Fibroma?

. Females in the first decade of life
. Males in their second and third decades of life
. Females in their fourth and fifth decades of life
. Males in their sixth and seventh decades of life
. Equal incidence across all age groups over 50

Correct Answer & Explanation

. Males in their second and third decades of life

Explanation

Chondromyxoid fibroma is a rare benign tumor that predominantly affects young adults in their second and third decades of life (teens to 20s), with a slight male predominance.

Question 6951

Topic: 10. Pathology and Oncology

A 52-year-old male presents with a permeative lytic lesion in the distal femur. Biopsy confirms primary bone lymphoma. Which of the following staging studies is most appropriate to confirm this is a primary bone lymphoma rather than metastatic systemic lymphoma?

. Bone marrow aspiration and biopsy, and a PET-CT scan
. Technetium-99m bone scan only
. Serum protein electrophoresis (SPEP)
. MRI of the entire neuroaxis
. 24-hour urine collection for Bence-Jones proteins

Correct Answer & Explanation

. Bone marrow aspiration and biopsy, and a PET-CT scan

Explanation

To diagnose Primary Bone Lymphoma, one must rule out systemic lymphoma that has simply metastasized to bone. Staging requires a PET-CT and bone marrow biopsy; primary bone lymphoma implies the lesion is limited to the bone (with or without regional lymph node involvement) for at least 6 months.

Question 6952

Topic: 10. Pathology and Oncology

A 45-year-old man presents with knee pain. Radiographs show a permeative lytic lesion in the distal femur. MRI reveals extensive marrow involvement and a large soft-tissue mass.

Biopsy demonstrates sheets of large round cells. Which of the following immunohistochemical markers is most likely to be positive in this lesion?

. CD20
. CD99
. Cytokeratin
. S-100
. Desmin

Correct Answer & Explanation

. CD20

Explanation

Primary bone lymphoma is most commonly Diffuse Large B-Cell Lymphoma (DLBCL), which stains positive for CD20 and CD45 (LCA). CD99 is typically positive in Ewing sarcoma, while cytokeratin indicates metastatic carcinoma.

Question 6953

Topic: 10. Pathology and Oncology

A 62-year-old male presents with deep, aching thigh pain. Radiographs reveal a permeative, moth-eaten lytic lesion in the femoral diaphysis. Biopsy demonstrates sheets of monotonous, small-to-medium round blue cells with prominent nucleoli and scant cytoplasm. Immunohistochemistry is strongly positive for CD20 and CD45, and negative for CD99. What is the most likely diagnosis?

. Ewing sarcoma
. Multiple myeloma
. Primary bone lymphoma
. Metastatic prostate carcinoma
. Chondrosarcoma

Correct Answer & Explanation

. Primary bone lymphoma

Explanation

Primary bone lymphoma (most commonly Diffuse Large B-Cell Lymphoma) presents as a permeative lytic lesion in older adults. Immunohistochemistry typically shows positivity for CD45 (LCA) and B-cell markers like CD20, distinguishing it from Ewing sarcoma (CD99+) and myeloma (CD138+).

Question 6954

Topic: 10. Pathology and Oncology

A 22-year-old male presents with persistent anterior leg pain. Radiographs show an eccentric, radiolucent lesion in the proximal tibial metaphysis with a well-defined sclerotic rim.

Histological examination reveals a lobular architecture with spindle and stellate-shaped cells in a myxoid background, with osteoclast-like giant cells clustered at the lobular peripheries. What is the recommended treatment?

. Observation
. Radiofrequency ablation
. Intralesional extended curettage and bone grafting
. Wide en bloc resection
. Neoadjuvant chemotherapy followed by wide resection

Correct Answer & Explanation

. Intralesional extended curettage and bone grafting

Explanation

The clinical, radiographic, and histologic findings (lobular pattern, stellate cells, myxoid stroma, peripheral giant cells) are diagnostic of Chondromyxoid Fibroma (CMF). The standard treatment for this locally aggressive benign tumor is extended intralesional curettage (with a high-speed burr) and bone grafting or cementing.

Question 6955

Topic: 10. Pathology and Oncology

A 65-year-old male presents with deep thigh pain. Radiographs reveal a permeative, destructive lesion in the femoral diaphysis with minimal periosteal reaction.

Biopsy shows sheets of atypical lymphoid cells. Which of the following is the most likely diagnosis?

. Multiple myeloma
. Ewing sarcoma
. Primary bone lymphoma
. Osteosarcoma
. Metastatic renal cell carcinoma

Correct Answer & Explanation

. Primary bone lymphoma

Explanation

Primary bone lymphoma, most commonly diffuse large B-cell lymphoma (DLBCL), typically presents in older adults as a permeative lytic lesion with minimal periosteal reaction. Biopsy demonstrating lymphoid cells confirms the diagnosis.

Question 6956

Topic: 10. Pathology and Oncology

A 55-year-old man presents with severe thigh pain. Radiographs appear largely unremarkable, but MRI demonstrates extensive diaphyseal marrow replacement. Biopsy shows sheets of round cells.

Which immunohistochemical marker is most diagnostic for the most likely condition?

. CD99
. CD20
. S-100
. Cytokeratin
. Desmin

Correct Answer & Explanation

. CD20

Explanation

Primary bone lymphoma is typically a diffuse large B-cell lymphoma, which strongly expresses CD20 and CD45 (LCA). CD99 is typically positive in Ewing sarcoma, while S-100 is seen in neural tumors and chondroid lesions.

Question 6957

Topic: 10. Pathology and Oncology

A 22-year-old man presents with chronic knee pain. Radiographs reveal an eccentric, lytic, metaphyseal lesion with a sclerotic margin in the proximal tibia. Histology shows lobules of myxoid and chondroid tissue with multinucleated giant cells at the periphery.

What is the most appropriate definitive management?

. Observation
. Simple intralesional curettage alone
. Extended intralesional curettage with high-speed burr and bone grafting
. Wide en bloc resection
. Neoadjuvant chemotherapy followed by resection

Correct Answer & Explanation

. Extended intralesional curettage with high-speed burr and bone grafting

Explanation

The diagnosis is Chondromyxoid fibroma (CMF), a benign but locally aggressive cartilage tumor. Simple curettage has an unacceptably high recurrence rate (up to 25-80% in older literature), making extended curettage with a high-speed burr and bone grafting the preferred treatment.

Question 6958

Topic: 10. Pathology and Oncology

An intraoperative frozen section of a lytic femoral lesion in a 55-year-old male demonstrates sheets of small round blue cells. The pathologist suspects primary bone lymphoma. What is the most critical step regarding the handling of the remaining biopsy specimen to confirm this diagnosis?

. Immediate decalcification with nitric acid
. Immersion in glutaraldehyde for electron microscopy
. Sending fresh tissue in normal saline or RPMI for flow cytometry
. Immediate freezing at -80 degrees Celsius
. Fixation in 10% buffered formalin exclusively

Correct Answer & Explanation

. Sending fresh tissue in normal saline or RPMI for flow cytometry

Explanation

Fresh tissue is required for flow cytometry and cytogenetic analysis, which are essential for definitively diagnosing and subtyping lymphoma. Putting the entire sample in formalin or decalcifying it will destroy cell surface markers needed for flow cytometry.

Question 6959

Topic: 10. Pathology and Oncology

A 48-year-old male presents with knee pain. Imaging reveals a diaphyseal permeative lesion in the distal femur. A biopsy is performed, and immunohistochemistry is positive for CD20 and CD45, and negative for CD99 and CD138. What is the most likely diagnosis?

. Ewing sarcoma
. Diffuse large B-cell lymphoma
. Multiple myeloma
. Metastatic carcinoma
. Chondrosarcoma

Correct Answer & Explanation

. Diffuse large B-cell lymphoma

Explanation

The immunohistochemical profile of primary bone lymphoma (usually Diffuse Large B-Cell Lymphoma) is positive for CD45 (Leukocyte Common Antigen) and CD20 (B-cell marker). Ewing sarcoma is CD99 positive, while multiple myeloma is CD138 positive.

Question 6960

Topic: Bone Tumors

A 50-year-old male presents with insidious thigh pain. Radiographs appear largely normal, but an MRI is obtained.

Which of the following MRI features is considered classic for primary bone lymphoma?

. Fluid-fluid levels on T2-weighted images
. A "dot-in-circle" sign on contrast-enhanced images
. Extensive marrow replacement and soft tissue mass out of proportion to cortical destruction
. The "penumbra sign" on T1-weighted images
. A distinct sclerotic rim surrounding a hyperintense nidus

Correct Answer & Explanation

. Extensive marrow replacement and soft tissue mass out of proportion to cortical destruction

Explanation

A hallmark of primary bone lymphoma is massive marrow involvement and soft tissue extension through cortical channels, producing minimal to no gross cortical bone destruction on plain radiographs.

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