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June 2021 – Bone and Soft Tissue Pathology Case 2

By MCL Education • June 14, 2021

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.