Infantile fibrosarcoma of femur.

We describe the clinical presentation and pathological features of an infantile fibrosarcoma of the femur that occurred in a 3 1/2-month-old male infant. The tumor grew rapidly, reaching large size within a few months, finally requiring amputation. The tumor was poorly circumscribed, infiltrating the adjacent soft tissue extensively. Microscopically, it was a highly cellular tumor composed of immature-appearing spindle-shaped cells. Ultrastructural study revealed mesenchymal cells with fibroblastic and histiocytic differentiation.