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

This post was developed by our Education and Technical Publications Team.