Primary Epithelioid Sarcoma of the Zygomatic Bone

Abstract

Primary epithelioid sarcoma of bone is extremely rare with only two reported cases in the English literature. A previously healthy 18-year-old male presented with a six-month history of right facial numbness and tingling and right eye diplopia. CT scan revealed an ill-defined mass with dense osseous matrix centered in the right zygomatic bone. An outside biopsy was read as osteosarcoma. The resection specimen revealed large epithelioid and spindle cells embedded in a prominent hyalinized matrix with focal metaplastic bone formation. The tumor cells were strongly and diffusely positive for AE1/AE3 and epithelial membrane antigen, but a definitive diagnosis of epithelioid sarcoma was not immediately reached due to the presence of dense hyalinized matrix and weak expression of SAT2B by tumor cells. Deficient INI1 protein expression by immunohistochemistry and homozygous loss of the SMARCB1 gene by chromosomal microarray analysis ultimately justified this tumor's designation as epithelioid sarcoma.

Genetic characteristics and molecular diagnostics of bone tumors

“…Epithelioid Sarcoma [129,130] Loss of SMARCB1 (INI1) secondary to biallelic loss of function mutations or heterozygous mutations in subunits of the SWI/SNF (BAF) complex Dysregulation of SWI/SNF (BAF) complex -involved in chromatin remodeling Sclerosing Epithelioid Fibrosarcoma/ Low-Grade Fibromyxoid Sarcoma [131][132][133] t(7;16)(q32-33;p11) t(11;16)(p11;p11)…”