June 2021 – Bone and Soft Tissue Pathology Case 2

A 29-year-old man presents with abdominal pain and is found to have a 5 cm presacral mass and vertebral metastasis.

Figure 1: BM-20X H&E Histologic sections of the metastatic vertebral lesion
Figure 2: BM-40X CD99 x2 Immunostaining for CD99

What genetic alteration is most characteristic for this malignancy?

  • BRAF v600e mutation
  • FUS-DDIT3 fusion
  • SS18-SSX1 fusion
  • EWSR1-FLI1 fusion

The correct answer is ...

The correct answer is: EWSR1-FLI1 fusion.

The histologic sections show a monotonous, small, round, blue cell neoplasm that is characteristic of Ewing’s sarcoma. The most common genetic alteration of Ewing’s sarcoma is EWSR1-FLI1 gene fusion, although alternative fusions between FET family genes and genes encoding for ETS-transcription factors have been described. The SS18-SSX1 gene fusion is found in synovial sarcoma. BRAF v600e mutations are found in a multitude of malignancies, including melanoma and papillary thyroid carcinoma, among others. FUS-DDIT3 gene fusion is found in myxoid liposarcoma.

Jeremy Molligan, M.D.

Senior Associate Consultant, Anatomic Pathology
Mayo Clinic

Jorge Torres-Mora, M.D.

Consultant, Anatomic Pathology
Mayo Clinic

Assistant Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science

MCL Education (@mmledu)

MCL Education

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