Primary leiomyosarcoma of bone--a clinicopathologic study of 8 uncommon cases with immunohistochemical analysis and clinical outcomes.

Primary leiomyosarcoma of bone is a rare and a diagnostically challenging tumor entity. Over a 7-year period, we identified 8 such cases that fulfilled the diagnostic criteria in 6 men and 2 women, with age ranging from 25 to 59 years (mean, 42.7 years). All cases were noted in the lower limbs, including femur and tibia as the commonly involved bones in 4 and 3 cases, respectively. On radiography, the most consistent feature was a solitary osteolytic lesion with cortical destruction, unassociated with matrix formation. On histopathology, all cases showed spindly sarcomatous cells, mostly arranged in fascicles and whorls. Of 8 cases, 6 (75%) were of high grade. Prominent vasculature was noted in 5 cases. Two cases displayed focal mineralization, including calcification and heterotropic woven bone formation in 1 case each, but lacked malignant osteoid or chondroid matrix. One case showed osteoclast-like giant cells. On immunohistochemistry, smooth muscle actin was diffusely positive in all cases (100%), desmin was positive in 6 (75%) of 8 cases, and h-caldesmon was positive in 5 (83.3%) of 6 cases. Five cases underwent surgery, including 3 amputations and 2 wide excisions. One case underwent chemotherapy. On follow-up, 5 cases developed metastasis, including 1 case with another, who died within 17 and 5 months. Leiomyosarcoma of bone is uncommon and diagnostically challenging. An index of suspicion is necessary for this diagnosis, especially in cases of lytic, destructive bone lesions, unassociated with matrix production, that show spindly sarcomatous cells on histopathology. Immunohistochemical analysis, including an optimum panel formed by smooth muscle actin (diffuse positivity), desmin, and h-caldesmon, is necessary for substantiating this diagnosis. Surgery forms the treatment mainstay. The prognosis appears to be dismal.