Primary intraosseous myoepithelioma arising in the iliac bone and displaying trisomies of 11, 15, 17 with del (16q) and del (22q11)--A rare case report with review of literature

Mixed tumors are uncommonly observed in the musculoskeletal system, where they form a common spectrum with a myoepithelioma and a parachordoma. Herein, we present a rare case of a mixed tumor/myoepithelioma arising in the iliac bone of a young adult male who presented with swelling in his right hip. Radiological imaging disclosed a large, intraosseous, lytic, heterogenous mass with a soft tissue component. Biopsy and subsequent tumor resection showed an 18 cm sized tumor involving the iliac bone and soft tissues and comprising polygonal and spindly cells, arranged in cords and aggregates, embedded in a myxohyaline stroma with osteochondroid differentiation. Tumor cells exhibited mild nuclear variation, rare mitotic figures, focal cytoplasmic clearing, and prominent squamous differentiation. On immunohistochemistry (IHC), tumor cells were diffusely positive for S100-P, EMA, CK5/6, p63, GFAP, calponin, and focally positive for CK/MNF116, but negative for Brachyury/T. Diagnosis of a myoepithelioma/mixed tumor was offered. Further, cytogenetic analysis revealed lack of EWSR1 gene rearrangement and showed clonal trisomies of 11, 15, 17 with del (16q) and del (22q11). The present case is a rare documentation of a myoepithelioma in the appendicular bones and the second such case identified in the iliac bone. IHC and cytogenetic findings supported a myoepithelial cell origin, and reinforced its relationship with a parachordoma and its distinction from mixed salivary gland tumors, a chordoma, and an extraskeletal myxoid chondrosarcoma that form its differential diagnoses.