Atypical fibroxanthoma distinguishable from spindle cell carcinoma in sarcoma-like skin lesions. A clinicopathologic and immunohistochemical study of 21 cases.

A clinicopathologic study was done of 21 cutaneous, sarcoma-like lesions previously diagnosed as atypical fibroxanthoma, spindle cell carcinoma, or dermal sarcoma. These lesions were most commonly presented as a solitary, often ulcerated nodule, occurring on exposed skin of the face in the elderly or, occasionally, on roentgen-damaged or burnt skin of the head, leg, or hand. Microscopic features of the 21 lesions were, however, not alike, thereby implying that such sarcoma-like lesions had derived from heterogeneous origins. The immunohistochemical staining in a comparative study with two other cases of unequivocal spindle cell squamous carcinoma suggested that these lesions could be histogenetically divided into two different groups: (1) the major group of true atypical fibroxanthoma, consisting of 19 cases, and (2) the minor group of probable spindle cell squamous carcinoma, consisting of 2 cases. Despite a wide histologic spectrum and of heterogeneity of these lesions, there was a benign clinical course in the majority, due in part to the small size and superficial location of the lesions.