Locally aggressive fibrous histiocytoma of bone. A case report.

A fibrohistiocytic tumour involving the distal diaphysis of the left femur in a 44-year-old woman is described. The lesion had a completely benign appearance cytologically but behaved in a locally aggressive manner in that it eroded the adjacent cortical bone and even extended into the soft tissue. To the best of our knowledge, no other similar case has been documented. A lesion of the humerus has been described as an atypical fibrous histiocytoma on the basis of prominent nuclear pleomorphism; the patient involved was alive 5 years after a disarticulation. The differential diagnosis of such a locally aggressive fibrous histiocytoma of bone would include a metaphyseal fibrous defect, benign fibroxanthoma, and malignant fibrous histiocytoma. We believe that the differentiation of a locally aggressive fibrous histiocytoma from the malignant variety may be important in view of the probable differing therapeutic and prognostic implications.