A Swedish study has found a rapid increase in the incidence of in situ and invasive squamous cell carcinomas with patterns suggesting a strong contribution from intentional skin tanning, according to an article in the July issue of the Archives of Dermatology.

According to the authors, squamous cell carcinoma of the skin was the fourth most common cancer in men and women in Sweden in 1998 and it has been the most rapidly increasing type of cancer there over the last 20 years.

Kari Hemminki, M.D., Ph.D., and her colleagues obtained cancer data from a national registry for the period from 1961 through 1998, which included 1,907 cases of invasive squamous cell carcinoma in children and 12,702 and 7,167 cases in fathers and mothers respectively. The numbers of patients affected by in situ squamous cell carcinoma were 2,666, 13,739, and 13,321, respectively.

The researchers found a large increase in reported cases of the disease, especially for the in situ type. Among cases of invasive carcinoma, the largest increase was seen on areas of the body usually covered by clothing, suggesting that the increase may be attributable to intentional tanning.

"In summary, our data show a large increase in reported cases of squamous cell carcinoma, of which in situ cases have increased drastically," the authors wrote. "Among invasive cases, the increase has been largest among covered sites, which also showed the largest cohort effect, suggesting contribution by intentional tanning. Familial risks of invasive and in situ skin cancers were equally large, and the familial effect was equally high on sun-exposed and covered sites."