Soft Tissue Lesions Practice Test

Dedifferentiated liposarcoma is defined by a tumor that contains areas of well-differentiated liposarcoma adjacent to or transitioning into a high-grade non-lipogenic sarcoma. This abrupt shift from lipogenic differentiation to a more aggressive, non-lipogenic appearance is the hallmark that distinguishes dedifferentiation. So seeing a well-differentiated liposarcoma component along with a high-grade, non-lipogenic area fits the defining pattern.

For context, the other options point to different tumors: the t(12;16) translocation is classic for myxoid liposarcoma; loss of INI1/SMARCB1 is associated with rhabdoid/epithelioid sarcomas; and CD31 positivity suggests a vascular tumor like angiosarcoma, not liposarcoma. (Note that MDM2 amplification is common in both well-differentiated and dedifferentiated liposarcomas, but the histologic hallmark described remains the mixed WDL and high-grade non-lipogenic area.)