Use of the Pill can offer cancer protection

Some risks increase when method used for 8+ years

Your patients may be asking you about research news that indicates that use of oral contraceptives (OCs) increase cancer risk for women who use the method for more than eight years.1

While the data are new, most of the women in the study used pill formulations that are no longer popularly prescribed in U.S. practices. According to a review of the most prescribed pills in the last 10 Contraceptive Technology Update Contraception Surveys, survey participants listed no pills above a 35 mcg dosage.

Most (75%) of the women in the current study used combined oral contraceptives containing 50 mcg of estrogen; 12% used pills with more than 50 mcg estrogen; 10% used pills with less than 50 mcg; and 3% used progestin-only pills. Most of the women used formulations from more than one category, with most moving over time to pills with less estrogen.

What prompted research?

Research in a 2006-published study prompted the current analysis.2 In that paper, scientists reported a significantly reduced risk of gynecological cancers combined among ever-users of oral contraceptives compared with never-users.2 The University of Aberdeen researchers used data from that oral contraception study to test the hypothesis that, compared with never-users, ever-users of oral contraception have a reduced overall risk of cancer.

To conduct the study, researchers from the University of Aberdeen in Scotland reviewed data between 1968 and 2004 collected by the Royal College of General Practitioners (RCGP) Oral Contraception Study, a large population-based dataset. The study recruited 46,000 women beginning in 1968. The average age for participants was 29. About half of the women were using oral contraceptives, and the other half had never used the method. Health care providers for the participants entered health information every six months on the women. Three-quarters of the women also were tracked by central registries so that their deaths and cancers were notified to the study even if they had left their recruitment health care provider. Researchers used the data to calculate the risk of developing cancer and also considered the effects of such variables as age, smoking, and social class.

Take a closer look

To perform the analysis, researchers used two sets of data. One set of data related to cancers reported while participants remained registered with their recruiting health care provider. The second main study dataset (the larger dataset) included cancers notified by central health registries after women had left their recruiting provider.

In both data sets, researchers report no overall increased risk of cancer among pill users, in spite of the high dosage of pills used in this study. When looking at the provider dataset alone, women who had taken the Pill at some time during their lives had a 3% reduced risk of developing any cancer. When the larger dataset was used, the reduction was 12%. In the central health registries dataset, women on OCs had statistically significant lower rates of large bowel/rectal, uterine body, and ovarian cancer. The provider dataset (the smaller dataset) showed a reduced risk of uterine and ovarian cancer.

For women who used oral contraceptives for more than eight years, who represented less than one-quarter of all pill takers, their risk was increased for being diagnosed with cancer, especially cancers of the cervix (adjusted relative risk 2.73, 1.61 to 4.61) and central nervous system or pituitary (5.51, 1.38 to 22.05). However, their odds of getting ovarian cancer were much lower (0.38, 0.16 to 0.88), with that protective effect lasting for at least 15 years after they stopped taking the Pill.1

What are the strengths of the study? Its cohort design allowed exposure information to be collected before cancer diagnosis, notes Philip Hannaford, MD, professor of primary care at the University of Aberdeen in Scotland and lead author of the research. Also, the study had a long follow-up period, so researchers were able to assess long-term effects. Its large numbers allowed calculations of risk estimates for many individual cancers, he reports.

Taking the Pill has important long-term benefits for most users, says Hannaford. While women who use the Pill for longer periods (eight years or more) may have a small increased risk for cancer, this risk does not affect most pill users, he notes. Three-quarters of the women in the current study had ceased use of the Pill prior to eight years, and this pattern probably exists today, Hannaford observes.

Most of the excess risk in long-term users was due to cervical cancer, he points out. The RCGP study began before comprehensive, regular cervical screening was started in the United Kingdom, so the risks probably were exaggerated, Hannaford notes. Such risks can be minimized by having a regular screen for cervical cancer, he says. "Pill users should be told not to be frightened to use the Pill, even for long durations, but they should have regular cervical cancer screens."

References

  1. Hannaford PC, Selvaraj S, Elliott AM, et al. Cancer risk among users of oral contraceptives: Cohort data from the Royal College of General Practitioner's oral contraception study. Br Med J 2007; 335:651.
  2. Vessey M, Painter R. Oral contraceptive use and cancer. Findings in a large cohort, 1968-2004. Br J Cancer 2006; 95:385-389.