Inflammatory fibrous histiocytoma. An aggressive and lethal lesion.

During an investigation of soft tissue fibrohistiocytic tumors, seven cases were found which we believe represent a new and specific diagnostic subgroup of fibrous histiocytomas. All patients were adults (mean 52.6 years), only one of whom was younger than age 40. There were four females and three males; all were Caucasian. The tumors which occurred in the retroperitoneum, anterior chest wall, anterior abdominal wall, femoral area, and oral cavity, were large, averaging 8.5 cm., and although appearing encapsulated, were microscopically infiltrative. The common histologic feature of all cases was a diffuse and at times intense neutrophilic infiltrate unassociated with tissue necrosis, in combination with bland and anaplastic appearing histiocytes. The presence of this acute exudative reaction is a unique feature of these lesions, and was present not only in the original tumors, but in recurrences and metastatic foci as well. Other cell types including foam cells, lymphocytes, plasma cells, eosinophils, Reed-Sternberg-like and ganglion-like cells were commonly present. A storiform fibrous pattern, a hallmark of the fibrous histiocytomas was seen at some time in all but one case. The treacherous aspect of these lesions was their bland initial histologic appearance. The foci of foam cells associated with the inflammatory elements often led to a diagnosis of a benign inflammatory reaction or xanthogranuloma. However, follow-up has confirmed the aggressive and neoplastic nature of these lesions. The clinical course was usually protracted with multiple recurrences and eventual metastases. All patients died of their tumor, the average survival being 53 months; four patients survived over 5 years. At this time, we propose the term inflammatory fibrous histiocytoma to designate these lesions.