Invasive squamous cell carcinoma arising from verrucous carcinoma. Recognition of verrucous carcinoma of skin as an in situ carcinoma.

In 1948, Ackerman first coined the term "verrucous carcinoma" to describe a variant of well-differentiated squamous cell carcinomas of the oral cavity. Similar lesions of the skin, other mucosa or mucocutaneous regions were subsequently reported. To date, verrucous carcinoma has been considered to be a variant of well-differentiated squamous cell carcinoma, which sometimes shows invasive changes but rarely metastasizes. In this study, findings for 3 patients with verrucous carcinomas in which foci of invasive squamous cell carcinoma existed are presented. Furthermore, the clinical features of 9 patients with verrucous carcinoma of the skin observed in our hospital between 1990 and 2004 are summarized. Lesions were located on the face, trunk or extremities. Foci of invasive squamous cell carcinoma were found in 30% of verrucous carcinomas, almost equal to the reported rate of verrucous carcinoma in oral or penile regions. Verrucous carcinoma of the skin should be recognized as a unique subtype of in situ carcinomas, which show exophytic nodular growth and are potentially malignant.