Spindle Cell Sarcoma With Novel JAZF1::NUDT5 Gene Fusion: Report of a Previously Undescribed Neoplasm

ABSTRACT Gene fusions involving JAZF1 are a recurrent event in low grade endometrial stromal sarcoma, and have been more recently described in few instances of endometrial stromal sarcoma‐like tumors in the genitourinary tract of men. In this article, we describe a previously unreported spindle cell sarcoma harboring an in‐frame JAZF1::NUDT5 gene fusion, arising in the chest wall of a 51‐year‐old man. The tumor had unique morphologic features resembling both endometrial stromal sarcoma and endometrial stromal sarcoma‐like tumors, consisting of a mixture of cytologically bland and pleomorphic spindle cells with brisk mitotic activity, within an alternating myxoid and fibrous stroma. It had diffuse immunohistochemical expression of CD10, CD34 and CD56, and variable expression of androgen receptor. To our knowledge, neoplasms with these clinico‐pathologic characteristics and novel gene fusion have not been previously reported in the English language literature.