There are more than 100 types of human papillomavirus (HPV). The most well-known types are sexually transmitted and cause genital warts, cervical cancer, and anal/genital tumors. But other HPV types spread easily without sexual contact and are a leading cause of non-genital warts, especially on the arms and fingers.
Earlier studies have linked some of these HPVs to skin cancer, especially in transplant patients on immune-suppressing therapy and in people with a genetic disease (epidermodysplasia verruciformis) that suppresses immune responses.
Now Margaret R. Karagas, PhD, of Dartmouth Medical School, and colleagues have taken these studies a step further. They looked for antibodies to 16 different skin HPV types in both cancer cases and non-cancer cases.
"We didn't find any high-risk types of HPV, as is the case for anal/genital cancer. But what we did find is a relationship between squamous cell carcinoma and the number of types to which someone tests positive," Karagas tells WebMD.
People with squamous cell skin cancers tended to have been infected with more skin HPV types, or cutaneous HPV, than those who did not have cancer, Karagas and colleagues found.
Moreover, there was evidence that people on long-term steroid medications for chronic conditions such as rheumatoid arthritis and asthma were at higher risk of HPV-associated skin cancer. These drugs have a mild, immunity-suppressing effect.
HPV, Warts, and the Immune System
What's happening? University of Miami dermatology professor Robert Kirsner, MD, notes that cutaneous HPV usually is kept in check by the immune system.
"Many people are exposed to cutaneous HPVs. Some develop warts," Kirsner tells WebMD. "But most people after a while -- and we don't know exactly what 'a while' means -- develop immunity against them. That's why warts are more common in children than in adults."
But isn't too much sun exposure the most likely trigger for skin cancer? Yes, says Kirsner. For at least two reasons: ultraviolet radiation triggers the transformation of normal cells into cancer cells. And UV radiation also suppresses the immune system in sensitive individuals, perhaps allowing HPV viruses to do their dirty work.
"So if you get this wart virus and are immune suppressed by UVB radiation, you can imagine how a cell could go from normal to carcinoma," Kirsner says.
But Kirsner and Karagas warn against jumping to conclusions. There's no proof that HPV truly causes skin cancer. It may be that the same risk factors that lead to skin cancer also lead to more HPV infections.
Even so, Karagas and colleagues note that their findings raise the possibility of preventing common skin cancers by preventing or treating HPV infection.
Karagas and colleagues report their findings in the July 8 Online First edition of BMJ. Funding came from the National Institutes of Health and the European Community; none of the authors report recent financial interest in companies that might have an interest in this work.