Abstract

Dermatofibromas or fibrous histiocytomas are common cutaneous lesions with histopathologic features characterized by a proliferation of spindled-shape fibrous cells in a storiform pattern, admixed with histiocytic cells in a stroma composed of collagen bundles and blood vessels. Clinically, they are often small and slow-growing. We report an unusual case of a 35-year-old woman with a cellular benign fibrous histiocytoma that presented as a rapidly growing, 2.5 cm fungating mass with surrounding induration on the back. Magnetic resonance imaging revealed a 4.9 x 3.5 x 1.3 cm enhancing mass involving the skin, subcutaneous tissue and fat. Clinical differential diagnosis included sarcoma, melanoma, metastatic carcinoma or B-cell lymphoma. Histopathology demonstrated a fibrohistiocytic and spindled proliferation with low mitotic activity. Immunohistochemical stains were notable for negative AE1/AE3, p63, SOX10, S100, STAT6, EMA and ALK1 with focal positivity for SMA, CD68 and factor XIIIa. Due to concern for an underlying malignancy, a wide local excision was performed. Additional histopathologic examination of the excised lesion confirmed the same characteristics and immunohistochemical stanning profile as the original. Cytogenetic study for PDGF-beta was negative supporting the diagnosis of cellular fibrous histiocytoma. This case is outstanding due to the impressive clinical presentation of a large and rapidly growing fungating mass. Awareness of the variability and potential large tumoral size is important for clinicians as they are evaluating these patients; histopathologic evaluation is crucial to distinguish these lesions from other entities.

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