Abstract

Ossifying fibromyxoid tumor (OFMT) is an uncommon mesenchymal neoplasm of uncertain differentiation and intermediate malignant potential. Recurrent PHF1 gene rearrangements are detected in up to 80% of OFMTs.  EPC1::SUZ12 gene fusion has been reported in endometrial stromal sarcoma but not in any other sarcoma. We report a case of digital OFMT with a novel EPC1::SUZ12 gene fusion.

A 69-year-old male presented with a 5-month history of a painless soft tissue mass on his right hand without any numbness and tingling in the right hand. Radiographic, histopathologic evaluation, immunohistochemical and NGS studies were performed.

Radiographic studies showed a peripherally heterogenous enhancing right-hand volar mass (3.9 x 2.6 x 2.0 cm) within the hypothenar compartment. Incisional biopsy showed an ossifying lesion containing round to oval cells with variable cytologic atypia in a fibromyxoid stroma. By immunohistochemistry, the cells were positive for SMA, CD99, SOX-11 and CD10 was positive and negative for S100 and SOX10. NGS was positive for EPC1::SUZ12 in-frame gene fusion involving EPC1 exon 10 fused to exon2 of SUZ12. The overall features were considered consistent with OFMT.

We describe a novel EPC1::SUZ12 gene fusion in digital OFMT. Further studies are warranted to elucidate the clinical significance of this gene fusion.