Histological diagnosis of cutaneous "warty" carcinoma on a pre-existing HPV lesion

A middle-aged man with an 8-year history of a fungating tumour mass on his thigh was histologically diagnosed as having an invasive "warty" carcinoma at the location of a pre-existing human papillomavirus (HPV) lesion. The tumour surface had a verruciform appearance with papillae containing fibrovascular cores. Many of the malignant cells displayed changes consistent with koilocytotic atypia. We noticed a greater degree of nuclear atypia in comparison with a verrucous carcinoma. Focally, some neoplastic cells demonstrated features of basaloid differentiation. Under in situ hybridization conditions, only HPV16 DNA, which is commonly associated with genital neoplasia, was detected selectively in rather superficial areas, corresponding to morphological evidence of HPV infection (i.e. koilocytotic atypia). It is worth noting that cutaneous location of such a warty carcinoma is very rare.