Low-grade myofibroblastic sarcoma of the distal femur

INTRODUCTION: Low-grade myofibroblastic sarcoma (myofibrosarcoma) is described to be a distinct atypical myofibroblastic tumor often with fibromatosis-like features and predilection for head and neck. Low-grade myofibroblastic sarcoma of bone is extremely rare. PRESENTATION OF CASE: A 50-year-old woman was admitted to our hospital because she had experienced right knee pain for 2 years. Plain radiography showed a honeycombed lesion on the right distal femur, and computed tomography showed a bone tumor with cortex destruction invading the soft tissue. A biopsy specimen from the intraosseous lesion showed a hypocellular area of spindle cell proliferation with dense collagen deposition, which is reminiscent of a histological feature of desmoplastic fibroma. However, histological examination of the extraosseous lesion indicated a slightly hypercellular area containing scattered spindle-shaped atypical cells with enlarged nuclei, suggestive of low-grade sarcoma. Spindle-shaped atypical cells were immunohistochemically positive for SMA. A final diagnosis of low-grade myofibroiblastic sarcoma of the bone was made from a surgically resected specimen. DISCUSSION: The patient was alive and well with no evidence of disease at 15 months after the surgery without any additional therapy. CONCLUSION: Extensive sampling of a tumor may be necessary to determine the true nature of the tumor and to make an accurate diagnosis.