To elucidate the risk factors for anal cancer, we interviewed and obtained blood specimens from 148 persons with anal cancer and from 166 controls with colon cancer in whom these diseases were diagnosed during 1978-1985. We found that in men, a history of receptive anal intercourse (related to homosexual behavior) was strongly associated with the occurrence of anal cancer (relative risk, 33.1; 95 percent confidence interval, 4.0 to 272.1). Anal intercourse was only weakly associated with the risk of anal cancer in women (relative risk, 1.8; 95 percent confidence interval, 0.7 to 4.2). Among the subjects with squamous-cell anal cancer, 47.1 percent of homosexual men, 28.6 percent of heterosexual men, and 28.3 percent of women gave a history of genital warts, as compared with only 1 to 2 percent of controls and no patients with transitional-cell anal cancer. In patients without a history of warts, anal cancer was associated with a history of gonorrhea in heterosexual men (relative risk, 17.2; 95 percent confidence interval, 2.0 to 149.4) and with seropositivity for herpes simplex type 2 (relative risk, 4.1; 95 percent confidence interval, 1.9 to 8.8) and Chlamydia trachomatis (relative risk, 2.3; 95 percent confidence interval, 1.1 to 4.8) in women. Current cigarette smoking was a substantial risk factor in both women (relative risk, 7.7; 95 percent confidence interval, 3.5 to 17.2) and men (relative risk, 9.4; 95 percent confidence interval, 2.3 to 38.5). We conclude that homosexual behavior in men is a risk factor for anal cancer, and that squamous-cell anal cancer is also associated with a history of genital warts, an association suggesting that papillomavirus infection is a cause of anal cancer. Certain other genital infections and cigarette smoking are also associated with anal cancer.
A larger study would allow examination of interrelationships of circumcision, infection with HPV, and smoking as risk factors.
The association between cigarette smoking and cervical cancer has been demonstrated in numerous prior studies. As part of population-based case-control studies of cancers of the vulva, vagina, cervix, anus, and penis in relation to infection with human papillomavirus, conducted in western Washington State and the province of British Columbia from the mid 1980s until the present time, the authors have collected detailed information on smoking history. The proportion of subjects who were current smokers of cigarettes ranged from slightly over 40% among incident cases of vaginal and cervical cancer to 60% among cases of vulvar and anal cancer. In contrast, only about 25% of controls were current smokers. The adjusted odds ratios (OR) associated with current smoking were substantially elevated (OR = 1.9-14.6) for all cancer sites except cancer of the vagina (OR = 1.3). The risks tended to increase in proportion to the number of cigarettes smoked. For most cancer sites, the odds ratios associated with former smoking were substantially less than those associated with current smoking and diminished with increasing time since cessation of smoking. The authors' data and those of other investigators suggest that cigarette smoking plays a role in the etiology of anogenital cancers and that smoking has a late-stage or promotional effect.
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