The prevalence of human papillomavirus genotypes in nonmelanoma skin cancers of nonimmunosuppressed individuals identifies high-risk genital types as possible risk factors.

Nonmelanoma skin cancer is the most commonly diagnosed malignant disease in Caucasians. Known risk factors include fair skin, sun exposure, male gender, advancing age, and the presence of solar keratosis. No viral risk factors have been established thus far. To examine the association between nonmelanoma skin cancer and infection with human papilloma virus (HPV) types, we performed a retrospective study in which skin biopsies were collected from 496 nonimmunosuppressed patients attending dermatologic clinics during a defined period and for whom a biopsy or resection of a tumor was indicated for medical reasons. A total of 390 patients with histologically confirmed diagnosis of warts (n = 209), solar keratosis or Bowen's disease (n = 91), squamous cell carcinoma (n = 72), or basal cell carcinoma (n = 18), as well as 106 control patients with normal skin was analyzed for infection with HPV and, if positive, HPV typed by sequencing. Logistic regression was performed to separately investigate association of certain HPV types with the occurrence of warts, precancerous lesions, and skin cancer compared with normal skin. For all three histological groups, both crude risk and risk adjusted for age, sex, and sun exposure were calculated. HPV DNA was detected in only 4.7% of controls, in 90.9% of benign warts, in 60.4% of precancerous lesions, in 59.7% of squamous cell carcinoma, and in 27.8% of basal cell carcinoma, which demonstrates that viral infection is specifically linked to skin disorders. The distribution of viral types found is distinctly different between warts and precancers or cancers, supporting an etiologic role of specific HPV types. This is supported by statistical analysis, where after adjusting for age, gender, and sun exposure, the odds ratio for nonmelanoma skin cancer in patients who were DNA positive for the high-risk mucosal HPV types, 16, 31, 35, and 51 was 59 (95% confidence interval, 5.4-645) with normal skin as controls. These findings suggest that persistent infections of the skin with high risk genital HPV types recently identified as significant risk factors for cervical cancer may also represent a risk factor for nonmelanoma skin cancer in a nonimmunosuppressed population.