Case-control study of cancer of the vulva.

A case-control study of 209 vulvar cancer patients and 348 community controls allowed assessment of risk factors for this rare tumor. As with cervical cancer, risk increased with the number of reported lifetime sexual partners, with five or more partners associated with two- to threefold increases in risk compared with zero to one partner. This factor largely explained the associations of risk with early age at first intercourse and low socioeconomic status. An independent association, however, was noted between vulvar cancer and a history of genital warts (relative risk 15.2; 95% confidence interval 5.5-42.1). Women who reported a previous abnormal Papanicolaou smear were at excess risk (relative risk 1.8), as were current smokers (relative risk 2.0). A significant interaction was noted between smoking and genital warts, with women reporting both having 35 times the risk of those with neither factor. Menstrual, reproductive, and hygiene factors were generally unrelated to risk. The relationships with sexual factors and genital warts support a common etiology for cervical and vulvar cancers. Future studies should focus on the etiologic agents for genital warts--the human papillomaviruses--and their enhancement by other factors, especially smoking and/or immune deficiencies.