Cutaneous papillary squamous cell carcinoma. A report of two cases.

Several histologic patterns of squamous cell carcinomas (SCC) have been described, including classical, adenoid, verrucous, and clear cell. We report 2 cases of an unusual purely exophytic papillary growth pattern. Both tumors occurred on sun-exposed skin of elderly patients and exhibited rapid growth. The tumors were red-tan and fungating, raising the clinical differential diagnoses of pyogenic granuloma, SCC, metastatic carcinoma or amelanotic melanoma. Histologically there was a prominent papillary growth pattern with several layers of notably atypical squamous epithelium overlying a fibro-vascular core in both cases. Mitoses were frequent. The tumors lacked deep invasion, although focal invasion of the stalk was present. These tumors were histologically distinct from verrucous carcinoma, verrucous Bowen's disease, and previously described adnexal carcinomas. The lack of deep invasion and the absence of local recurrence or metastatic disease after 18 months follow-up suggest that this histologic variant is a low-grade malignancy, although study of more cases and longer follow-up will be necessary to accurately assess the biology of this papillary variant of SCC. We believe that this growth pattern has not yet been described and a pure papillary form must be included as one of the histological subtypes of cutaneous SCC.