Oral Contraceptives and Cancer Risks

By Frederick R. Jelovsek, M.D.

Most women are unaware that birth control pills are one of the few medicines that actually prevent cancer. In fact, 30-40% think that pills increase the risk of cancer. It is important to know the numbers. These have been coalesced in a recent article by Kaunitz and Benrubi in Kaunitz, AM, Benrubi GI: The good news about hormonal contraception and gynecologic cancer. The Female Patient 1998;23:43-51.

Last year approximately 256,000 women had the new diagnosis of breast, endometrial, ovarian and cervical cancer. About 69,000 women died. Let's put the different cancers in perspective:

Breast cancer has been studied extensively. There is thought to be a slight increase in the risk of breast cancer associated with birth control pills and also probably with the injectable contraceptive, depo-medroxyprogesterone acetate (Depoprovera®). The increase is a risk ratio about 1.3 and the risk decreases to 1.0 after 10 years.

Endometrial cancer has a large reduction (50%, risk ratio 0.5) when oral contraceptives are used and this effect may last up to 20 years after discontinuing the pills. Depoprovera® reduces endometrial cancer even more, up to 80% -- so much so that it is sometimes used as a treatment for endometrial cancer.

Ovarian cancer is the most lethal of the female reproductive malignancies. Oral contraceptives, however, significantly reduce the incidence by 40% and it may be as much as 80% in women who have used the pill 10 years or longer. It appears that the benefit has something to do with inhibiting ovulation of the ovary(s) each month because pregnancy and lactation, both of which reduce ovulations, are also factors which lower risk. On the other side, ovulation induction medicines such as clomiphene citrate, which is used to cause ovulation in infertility patients, is suspected of slightly increasing the risk of ovarian cancer.

Cervical cancer is present more often in contraceptive pill users than nonusers. This results in an increased risk ratio of about 1.5-1.9. An uncommon form of cervical cancer, adenocarcinoma, also shows an increased risk ratio of about 2.0-2.5 with pill use. We must remember, however, that cervical cancer is a sexually transmitted disease that is increased by having multiple sexual partners and is decreased by using barrier contraceptives such as condoms. Many physicians think that the excess risk for cervical cancer due to pills merely represents its comparison to non-pill users who predominantly use barrier contraceptives. No scientific studies have yet confirmed or denied this.

The following table tries to sum these different findings, but remember, this is an artificial summation just for thought.

You can see from the above table why many women may be justified in their belief that oral contraceptives increase the risk of cancer. Even if cervical cancer is excluded, they may be right! Oral contraceptive decisions should take into account family history of cancer.