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Pathology · USMLE Step 1

USMLE Pathology: Soft Tissue Tumors

Soft tissue sarcoma classification and morphology, distinct from the bone-tumor focus of the musculoskeletal and dermatologic pathology deck.

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What is the most common soft tissue sarcoma in adults overall?
Liposarcoma
What is the most common soft tissue sarcoma in children?
Rhabdomyosarcoma
Well-differentiated liposarcoma is characterized by amplification of which gene?
MDM2
What chromosomal translocation and fusion gene characterize myxoid liposarcoma?
t(12;16) producing a DDIT3-FUS fusion
Myxoid liposarcoma shows what characteristic vascular pattern on histology?
A branching, 'chicken-wire' pattern of thin capillaries within myxoid stroma
How does pleomorphic liposarcoma compare in grade to other liposarcoma subtypes?
It is the highest-grade liposarcoma subtype
Which rhabdomyosarcoma subtype is the most common overall?
Embryonal rhabdomyosarcoma
Embryonal rhabdomyosarcoma most commonly arises in which body regions?
The head and neck, and the genitourinary tract
What is the botryoid variant of embryonal rhabdomyosarcoma?
A grape-like mass arising in hollow organs such as the vagina or bladder
What translocation and fusion gene characterize alveolar rhabdomyosarcoma?
t(2;13) producing a PAX3-FOXO1 fusion
How does alveolar rhabdomyosarcoma differ from embryonal rhabdomyosarcoma in site and prognosis?
It typically arises in the extremities of adolescents and carries a worse prognosis
Which two immunohistochemical markers confirm rhabdomyoblast (skeletal muscle) differentiation?
Desmin and myogenin
What morphologic feature is classic for a rhabdomyoblast on H&E?
Eosinophilic cytoplasm with visible cross-striations
What are the two most common anatomic sites for leiomyosarcoma?
The retroperitoneum and the uterus
What nuclear feature characterizes the spindle cells of leiomyosarcoma?
Blunt-ended, 'cigar-shaped' nuclei

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