Pleomorphic fibroma of the skin: a benign neoplasm with cytologic atypia. A clinicopathologic study of eight cases.

A clinicopathologic study of eight examples of polypoid and dome-shaped cutaneous fibrous lesions with sparse cellularity but striking nuclear atypia and rare mitotic figures is presented. Positive immunohistochemical staining for vimentin and actin supported the fibroblastic nature of these lesions. All eight cases were adults whose ages ranged from 33 to 67 years (mean 52 years). Five were women and three were men. Five lesions were located on extremities, two on the trunk, and one on the face and they measured from 4 to 16 mm in greatest dimension. The lesions were clinically followed from 4 months to 5 years. They all showed benign clinical behavior, with only one local recurrence in a lesion that had been incompletely removed. The nuclear atypia seen in these fibrous lesions may be similar to that which occurs in other benign mesenchymal neoplasms, such as pleomorphic lipoma, pleomorphic leiomyoma, ancient schwannoma, and variants of dermatofibroma with atypical cells. We suggest that "pleomorphic fibroma" is an appropriate term for this lesion based on its histologic differentiation, cytologic atypia, and benign clinical course.