Tubal ligation and incidence of 26 site-specific cancers in the million women study

The risk of ovarian cancer is reduced in women who undergo tubal ligation. Although it has been suggested that tubal ligation is also associated with reduced risk of breast, endometrial, and cervical cancers, there is no clear evidence for these tumors. The Million Women Study is a prospective study that investigated associations for 26 site-specific cancers among 1.3 million UK women enrolled in 1996–2001. At enrollment, participants completed a questionnaire on sociodemographic, reproductive, and lifestyle factors; follow-up outcomes for cancer and death were obtained from national registries. Cox regression models were used to estimate adjusted relative risks (aRRs) of developing 26 cancer types or sites among women with and without tubal ligation. Of 1,278,783 women without previous cancer, 167,430 developed incident cancers after a mean follow-up of 13.8 years. Risks were significantly reduced in women with tubal ligation for cancers of the ovary (aRR, 80; 95% confidence interval [CI], 0.76–0.85; P < 0.001; n = 8035), peritoneum (aRR, 0.81; 95 CI%, 0.66–0.98; P = 0.03; n = 730), and fallopian tube (aRR, 0.60; 95 CI%, 0.37–0.96; P = 0.04; n = 168). There were no significant associations for cancers of the breast, endometrium, or cervix. The findings are consistent with the hypothesis that cancers of the ovary, peritoneum, and fallopian tube have a shared origin in the fallopian tube and that tubal ligation reduces cancer risk. These data, as well as findings of other investigators, suggest that the fallopian tube is a barrier to cells, carcinogens, or other agents reaching the ovary and peritoneal cavity.