Desmoplastic seborrheic keratosis

Eleven cases of seborrheic keratoses with desmoplastic stroma and associated nests and cords of squamous epithelium simulating infiltrating carcinoma are presented. There were 7 males and 4 females ranging in age from 44 to 88 years (mean = 62). Eight cases were on the head and neck, one each on the lower and upper extremity, and one on the pubic area. Clinical diagnoses included seborrheic keratosis, squamous and basal cell carcinoma, and dermal nevus. Histologically, the lesions were characterized by exophytic growth pattern of basaloid and squamous cells, without cytologic atypia, and well-demarcated peripheral borders, typical for that seen in seborrheic keratoses. Squamous eddy formation with parakeratosis and spongiosis was present in all cases. Located within the body of the lesions were irregular nests and cords of squamous cells extending into the surrounding dermis with associated fibroblastic dermal proliferation trapping the epithelial nests, simulating invasive carcinoma. Immunohistochemically, the epithelial nests were cytokeratin positive and HPV negative, and the dermal stromal cells were vimentin positive and factor XIIIa, cytokeratin, and CD34 negative. Adjacent changes of carcinoma, trichilemmoma, verruca, or other adnexal neoplasm were not identified. Seborrheic keratoses may demonstrate desmoplastic changes analogous to that seen in desmoplastic trichilemmomas. Awareness of these changes in seborrheic keratosis will avoid misdiagnosis and excessive therapy.