Osseous Leiomyosarcoma: A Rare Entity

ABSTRACT Leiomyosarcomas represent a group of aggressive soft-tissue sarcomas arising from smooth muscle cells primarily found in the uterus and gastrointestinal tract. Leiomyosarcomas of the bone are extremely rare. We report a rare case of leiomyosarcoma of the tibia. A 71-year-old male patient presented to our department with the chief complaint of painful swelling over the left knee for 3 months. Magnetic resonance imaging (MRI) with gadolinium of the left knee showed a 7.5 cm × 6 cm × 5 cm bony lesion associated with a soft-tissue component in the upper epimetaphysis of the left tibia. A biopsy of the lesion showed a malignant spindle cell tumor, following which the patient was offered two cycles of adriamycin single-agent chemotherapy. Postchemotherapy MRI showed progression of the lesion to the size of 9.9 cm × 8.2 cm × 6.5 cm, involving the articular surface of the tibia. Following progression, the patient was planned for wide local excision of the lesion, which turned out to be leiomyosarcoma Grade III with a mitotic rate of 30/10 high power field, and the size of the lesion’s largest diameter was 8 cm with soft-tissue infiltration. Margins were clear, and there were no adverse features of lymphovascular and perineural invasion or articular cartilage infiltration. Immunohistochemistry markers were used to confirm the bony origin of the leiomyosarcoma, which is extremely rare. Actin, calponin, and S 100 were positive, and CD 34, SOX 10, and SATB2 were negative. All surgical slides examined showed no evidence of osteoid. Postoperative positron emission computed tomography revealed no evidence of any disease, and thereby, the plan was to keep the patient on close follow-up. Multiple studies have reported a poor response of leiomyosarcoma of the bone to chemotherapy, as well as minimal overall survival benefit. The radical surgical excision of a bony lesion with the achievement of negative margins is similar to that of other primary malignant bone tumors. Sarcomas are generally believed to be radioresistant in nature, and thereby, their role in either a neoadjuvant or adjuvant setting is controversial. A multidisciplinary approach should be used in such rare cases as leiomyosarcomas of osseous origin.