Gynaecological surgical procedures and risk of colorectal cancer in women

This study explored the relationship between certain gynaecological procedures and the risk of colorectal cancer in Ontario women, The cohort comprised all women undergoing gynaecological surgery for tubal ligation, unilateral and bilateral oopherectomy, and hysterectomy between 1979 and 1993 in Ontario. Person-years were calculated until death, a cancer diagnosis, or the end of the study period, after linkage to the Ontario Cancer Registry and the Ontario mortality file. Relative risk estimates were based on comparing observed and expected cancers in the cohort, the expected based on population incidence rates. In a cohort of more than 730,000 women, mean follow-up time was approximately 7.5 years. The risk of colorectal cancer was reduced following certain of the surgical procedures, Relative risk (RR) estimates for bilateral tubal sterilization [RR = 0.81; 95% confidence intervals (CI) = 0.70-0.93], hysterectomy (RR = 0.89; 95% CI = 0.81-0.97) and hysterectomy with bilateral salpingo-oophorectomy (RR = 0.84, 95% CI = 0.75-0.94) all were substantially lower than 1.0, while neither unilateral oophorectomy nor tubal sterilization yielded risks different from 1.0. No pattern of altered risk was evident across age groups or over time since the surgical procedure. While there is potential for uncontrolled confounding by such exposures as hormone replacement therapy, the observed risks are consistent with a hypothesis of lowered endogenous oestrogen levels being associated with reduced risk of colorectal cancer. (C) 1999 Lippincott Williams & Wilkins.