The Pill’s Cancer Protection Confirmed

OC use for fewer than 8 years did not increase overall cancer rates, and it reduced gynecologic cancer risk in British women.
To investigate cancer risk among users of oral contraceptives (OCs), researchers analyzed 36 years of data from the U.K. National Health Service (NHS) and participating British general practitioners on OC use and incidence of various cancers. The study included 745,000 and 339,000 woman-years of observation for OC ever-users and never-users, respectively (NHS dataset), and 331,000 and 224,000 woman-years for ever-users and never-users, respectively (GP dataset).
The NHS data showed that ever-users of OCs had statistically significant relative risk reductions of 12% for any type of cancer and 30% for gynecologic cancers compared with never-users. The GP data demonstrated a 3% generalized cancer risk reduction (not statistically significant) and a 20% gynecologic cancer risk reduction in ever-users (of marginal statistical significance). Neither cohort showed a difference in risk for breast cancer for ever-users versus never-users. In both ever- and never-users, the rate of any cancer increased with age and smoking. Prolonged use of OCs (>8 years) reduced ovarian cancer risk by 62% but increased the risk for any cancer by 20%. In particular, prolonged OC use more than doubled the risk for cervical cancer (risk ratio, 2.73; 95% confidence interval, 1.61–4.61) and increased fivefold the risk for central nervous system and pituitary cancers (RR, 5.51; 95% CI, 1.38–22.05).
Comment: In more than 80% of OC users in this study, the formulations were high-dose (50 µg estrogen); whether similar risk reductions would occur with lower estrogen doses is uncertain. Nonetheless, women can be reassured that fewer than 8 years of OC use seems to be beneficial in cancer prevention, especially for ovarian and uterine cancers, and does not affect breast cancer risk.
— Wendy S. Biggs, MD
Published in Journal Watch Women's Health October 18, 2007
Citation(s):
Hannaford PC et al. Cancer risk among users of oral contraceptives: Cohort data from the Royal College of General Practitioners’ oral contraception study. BMJ 2007 Sep 29; 335:651.