Contraceptive Procedure Can Reduce the Risk of Specific Subtypes of Ovarian Cancer

Subgroup analysis from a large prospective cohort study conducted in the United Kingdom evaluated the association between the risk of ovarian cancer and tubal ligation in over 8000 women who had developed the tumor. The result: strong evidence that the risk of ovarian cancer associated with tubal ligation varied by tumor histotype—while the risk of serous tumors saw a moderate reduction following the procedure, a more detailed analysis pointed to a 20% reduction in risk of high-grade serous carcinoma but no effect on the risk of low-grade serous tumors.

The cohort evaluated for this analysis published in the International Journal of Cancer was part of a much bigger study that includes 1.3 million UK women recruited between 1996 and 2001 UK National Health Service (NHS) Breast Screening Program. For the analysis, the authors write that the outcome of interest, ovarian cancer, was split into 5 histological groups: serous, mucinous, endometrioid, clear cell, and other. Each subgroup was further divided into grades. Women included in the study were asked if they had been sterilized by tubal ligation (tube tying), the variable whose influence was evaluated in this specific analysis.

Of the 1,132,914 women who were recruited, about 22% (246,048) affirmed having had a tubal ligation at a median age of 35 years. In terms of demographics, the author write that women who reported a previous tubal ligation were more likely to be parous, to have used the oral contraceptive pill and menopausal hormones, to have had a hysterectomy, to be a current smoker, and to live in areas in the lower third of socioeconomic status, compared with women without tubal ligation. During the average follow-up period of 13.8 years, 8035 incident ovarian cancers were reported:

· 3515 (44%) were serous

· 836 (10%) were mucinous

· 690 (9%) were endometrioid

· 401 (5%) were clear cell

· 2593 (32%) were of other histological types (mostly unspecified epithelial tumors).

With the mean age at diagnosis of 65.1 years, the authors found the relative risk of ovarian cancer among women with tubal ligation was 0.80 (95% confidence interval, CI: 0.76-0.85, P<.001), compared with women who had not undergone the contraception procedure. More significantly, a strong influence of tumor histotype was observed: while the risk of clear cell and endometrioid tumors reduced by half, risk of serous tumor reduced by a small, yet significant, amount. However, the development of mucinous tumors was not affected by the status of tubal ligation in these women. Further, there was strong evidence that tubal ligation was associated with a reduction in the risk of high-grade serous carcinoma (n&thinsp;=&thinsp;1593; relative risk, RR: 0.77; 95% CI: 0.67-0.89), but not of low-grade serous tumors (n = 447; RR: 1.13; 95% CI: 0.89-1.42).

Pointing to the significance of their findings, the authors suggest a rethinking of the origins of these cancers.

“For the reduced risk seen among women with tubal ligation—it could be that tubal ligation acts as a barrier to help prevent the abnormal cells that might cause these tumors passing through the fallopian tubes to the ovaries. Our results are really interesting, because they show that the associations with known risk factors for ovarian cancer, such as childbirth and fertility, vary between the different tumor types,” according to Kezia Gaitskell, DPhil candidate at the University of Oxford and first author on the study.