A case of atypical fibrous histiocytoma with positivity for CD163 and CD44.

Atypical fibrous histiocytoma (AFH) is a variant of der-matofibroma (DF) that was first described by Fukamizu et al. (1) in 1983. Histologically AFH is characterized by proliferation of dermal spindle cells composed mainly of atypical histiocytic cells with striking nuclear pleo-morphism and atypia, in a background of classic fibrous histiocytoma (2). It is known that many cases of AFH follow a benign course if complete excision is carried out (2, 3). However, because the tumour cells are atypical, AFH must be differentiated from tumours of intermediate malignancy, such as dermatofibrosarcoma protuberans (DFSP) or atypical fibrous xanthoma (AFX), as well as more malignant tumours, such as pleomorphic dermal sarcoma (PDS)/malignant fibrous histiocytoma (MFH). We report here a case of AFH on the left upper arm of a 63-year-old woman and describe its immunoreactivity in detail. We also discuss the points of histological and immunohistological differentiation between AFH and other cutaneous spindle cell tumours. A 63-year-old woman presented with an 8-month history of a symptomless, slowly growing swelling on the left upper arm. The patient had no unusual medical or family history. Clinical examination revealed an 8-mm black-purplish hard mass with peripheral erythema (Fig. 1A). The tumour had arisen at a site without any known previous history of injury. A haemangioma was clinically suspected, and surgical excision was performed. Microscopic examination revealed a well-defined lesion, located in the dermis and extending to the subcutaneous tissue, with epidermal hyperplasia and a grenz zone (Fig. 1B). The lesion was composed largely of interlacing fascicles of predominant histiocyte-like eosinophilic spindle cells with elongated or plump vesicular nuclei, arranged in a storiform pattern. Abundant pleomorphic giant cells with huge bizarre nuclei (bi-lobed and multi-lobed) and histiocytes with large vesicular nuclei and prominent eosinophilic nucleoli were observed (Fig. 1C). In the peripheral region of the tumour, fibroblast-like spindle cells arranged in a storiform or fascicular pattern with collagen bundles were observed, resembling the classic features of DF. No necrosis was present. Foci of chronic inflammatory cells, including lympho cytes and plasma cells, were also evident. As a typical feature, we noted individual prominent hyalinized collagen bundles surrounded by tumour cells, predominantly in the periphery of the lesion (Fig. 1D). The mitotic count was 3 per 10 high-power fields (HPF). Immunohistochemical staining revealed diffuse positivity for vimentin, factor XIIIa, CD68, CD163 (Fig. 1E) and CD44 (Fig. 1F). The lesion showed no reactivity for desmin, CD34, AE1/AE3, desmin, S-100 …