Ovarian cancer risk of Hormonal Contraception

The incidence of ovarian cancer is reduced by pregnancy, lactation, tubal ligation and oral contraceptives ⁽²⁴⁾. The role of sex hormones seems important for ovarian carcinogenesis.

Epidemiological observations and experimental data from the animal model indicate that estrogens may have an adverse effect, while progesterone/progestins reduce the effect directly on the ovarian epithelium. There is evidence that oral contraceptive use provides substantial protection against ovarian cancer and that the longer HC use offers the greater reduction in ovarian cancer risk (p< 0.001) ^(17,25).

However, the eventual public-health effects of this reduction will depend on how long the protection lasts after use ceases. Women who have used oral contraceptives for 5 years or longer, have about half the risk of ovarian cancer compared with never users ^(26,27,28).

Recently, the Collaborative Group on Epidemiological Studies of Ovarian Cancer (Oxford) reported from a reanalysis of data from 45 epidemiological studies including 23,257 women with ovarian cancer and 87,303 controls that this reduction in risk persisted for more than 30 years after oral contraceptive use had ceased.However,it became somewhat attenuated over time; the proportional risk reductions per 5 years of use were 29% for use that had ceased less than 10 years previously, 19% for use that had ceased 10-19 years previously, and 15% for use that had ceased 20-29 years previously. This effect is not dose-dependent considering the similar proportional risk reduction from the 1960s onwards ⁽²⁹⁾.

The incidence of mucinous tumours (12% of the total) seemed little affected by oral contraceptives, but otherwise the proportional risk reduction did not vary much between different histological types.
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These findings suggest that oral contraceptives have already prevented some 200,000 ovarian cancers and 100,000 deaths from the disease, and that over the next few decades the number of cancers prevented will rise to at least 30,000 per year ^{(18, 29 )}. The reduction of risk does not seem related to androgenicity of the hormonal contraceptives ^(27,30). Low-estrogen dose oral contraceptives confer a benefit, regarding ovarian cancer risk, similar to that conferred by earlier high-estrogen-dose formulations ^(31,32,33).

While, current available data suggest that long-term use of estrogens may slightly increase the risk, especially of endometrioid type of ovarian cancer ^(3,30). The protective effect of combined oral contraceptive pill, was confirmed in multiple studies; however, it is unclear whether this protection also covers women with a genetic predisposition to ovarian cancer or perimenopausal women. About 5% of all ovarian-cancer cases are caused by a genetic predisposition, in particular as a component of the autosomal dominant hereditary breast-ovarian-cancer syndrome.