Tubal ligation and incidence of 26 site-specific cancers in the Million Women Study.

Background: Tubal ligation is known to be associated with a reduction in ovarian cancer risk. Associations with breast, endometrial and cervical cancers have been suggested. We investigated associations for 26 site-specific cancers in a large UK cohort.

Methods: Study participants completed a questionnaire on reproductive and lifestyle factors in 1996-2001, and were followed for cancer and death via national registries. Using Cox regression models, we estimated adjusted relative risks (RRs) for 26 site-specific cancers among women with vs without tubal ligation.

Results: In 1 278 783 women without previous cancer, 167 430 incident cancers accrued during 13.8 years' follow-up. Significantly reduced risks were found in women with tubal ligation for cancers of the ovary (RR=0.80, 95% CI: 0.76-0.85; P<0.001; n=8035), peritoneum (RR=0.81, 0.66-0.98; P=0.03; n=730), and fallopian tube (RR=0.60, 0.37-0.96; P=0.04; n=168). No significant associations were found for endometrial, breast, or cervical cancers.

Conclusions: The reduced risks of ovarian, peritoneal and fallopian tube cancers are consistent with hypotheses of a common origin for many tumours at these sites, and with the suggestion that tubal ligation blocks cells, carcinogens or other agents from reaching the ovary, fallopian tubes and peritoneal cavity.