Cutaneous Fibrohistiocytic Tumors

Abstract
This review summarizes the clinicopathologic features of the so-called cutaneous “fibrohistiocytic” tumors, a descriptive term for a group of heterogeneous lesions that have in common cells that, on light microscopy, resemble fibroblasts and histiocytes. Emphasis is placed on the less well-known variants of cutaneous fibrous histiocytoma, namely: cellular benign fibrous histiocytoma, a lesion that histologically mimics dermatofibrosarcoma protuberans and leiomyosarcoma; aneurysmal (“angiomatoid”) benign fibrous histiocytoma, clinically resembling a melanocytic or vascular lesion and histologically often confused with a vascular tumor or with angiomatoid malignant fibrous histiocytoma; epithelioid benign fibrous histiocytoma, characterized histologically by plump angulated eosinophilic cells with prominent nucleoli and often confused with a Spitz nevus; and atypical (pseudosarcomatous) benign fibrous histiocytoma, characterized by bizarre pleomorphic histiocyte-like or multinucleated cells and sometimes misdiagnosed as a malignant tumor. Mention is also made of lipidized benign fibrous histiocytoma, a lesion that tends to present around the ankle and mimics a xanthoma histologically; palisading fibrous histiocytoma, which shows histologically prominent nuclear palisading as seen in schwannoma, and atrophic dermatofibroma, which probably represents an “old” hyalinized fibrous histiocytoma. Also discussed in this review are plexiform fibrohistiocytic tumor, a recurring lesion located mainly in the limbs, characterized by an infiltrative growth pattern and varying proportions of fibroblastic fascicles interspersed with nodules of histiocyte-like cells, and atypical fibroxanthoma, a histologically malignant but clinically benign superficial tumor arising in sun-exposed areas of the elderly. The existence of a “non-pleomorphic” spindle-celled variant of this tumor is emphasized; clinicopathologic correlation and immunohistochemistry are essential for its diagnosis. So-called “pleomorphic malignant fibrous histiocytoma,” which we believe is a wastebasket term for a heterogeneous group of histologically high-grade malignant neoplasms involving the skin, is mentioned only briefly.