Bone tumours: MDM2 in well-differentiated liposarcoma: practice question

A Orthopaedics question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Orthopaedics · Bone tumours: MDM2 in well-differentiated liposarcoma

Sample item

A 60-year-old has a large, deep, painless thigh mass that is mostly mature fat with thick septa and nodular non-fatty areas on MRI. To distinguish a well-differentiated liposarcoma from a lipoma, which molecular test is most useful?

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

A. MDM2 amplification by FISH

Well-differentiated liposarcoma carries amplification of MDM2 (with CDK4) on chromosome 12q13-15, which is absent in lipoma. Deep location and thick septa raise suspicion. FUS-DDIT3 marks myxoid liposarcoma, SS18-SSX marks synovial sarcoma, and EWSR1-FLI1 marks Ewing sarcoma.

Option by option

  • A. MDM2 amplification by FISH (correct)

    Correct. MDM2 amplification confirms an atypical lipomatous tumour or well-differentiated liposarcoma.

  • B. EWSR1-FLI1 fusion

    EWSR1-FLI1 is the translocation of Ewing sarcoma.

  • C. SS18-SSX fusion

    SS18-SSX is the translocation of synovial sarcoma.

  • D. FUS-DDIT3 fusion

    FUS-DDIT3 is the translocation of myxoid liposarcoma.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

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Questions about this Orthopaedics question

What is the answer to this Orthopaedics question?

The best answer is A, MDM2 amplification by FISH. Well-differentiated liposarcoma carries amplification of MDM2 (with CDK4) on chromosome 12q13-15, which is absent in lipoma.

Why is "EWSR1-FLI1 fusion" not the answer?

EWSR1-FLI1 is the translocation of Ewing sarcoma.

Why is "SS18-SSX fusion" not the answer?

SS18-SSX is the translocation of synovial sarcoma.

Why is "FUS-DDIT3 fusion" not the answer?

FUS-DDIT3 is the translocation of myxoid liposarcoma.

What concept does this question test?

It tests Bone tumours: MDM2 in well-differentiated liposarcoma in Orthopaedics. Deep location and thick septa raise suspicion. FUS-DDIT3 marks myxoid liposarcoma, SS18-SSX marks synovial sarcoma, and EWSR1-FLI1 marks Ewing sarcoma.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Bone tumours: MDM2 in well-differentiated liposarcoma?

Pair each fracture with its classic complication and nerve injured. Then use the flashcards and the other Orthopaedics questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.