Research Affirms Protective Benefit of Oral Contraceptives
EXECUTIVE SUMMARY
The latest findings from a long-term study conducted in the United Kingdom indicate that most women who choose to use oral contraceptives do not expose themselves to long-term cancer harms. For some cancers, many women benefit from important reductions of risk that persist for many years after they stop taking the Pill.
- Analysts looked at the U.K.-based Royal College of General Practitioners’ Oral Contraception Study, which recruited 46,022 women in 1968 and 1969 for observation for up to 44 years.
- Ever-use of the Pill was associated with reduced risks of colorectal, endometrial, and ovarian cancer.
Reassuring news for women: The latest findings from a long-term study indicate that most women who choose to use oral contraceptives do not expose themselves to long-term cancer harms.1 For some cancer types, many women benefit from important reductions of risk that persist for many years after stopping use of the Pill.1
The purpose of the study was to examine the long-term cancer risks or benefits associated with the use of combined oral contraceptives, including the estimated overall lifetime balance. Analysts looked at the U.K.-based Royal College of General Practitioners’ Oral Contraception Study, which recruited 46,022 women in 1968 and 1969 for observation for up to 44 years. Directly standardized rates of specific cancer and any cancer were calculated for ever- and never-users of combined oral contraceptives. Data were standardized for age, parity, social class, and smoking. Attributable risk and preventive fraction percentages were calculated for the report.
Findings from the analysis indicate there were 4,661 ever-users with at least one cancer during 884,895 woman-years of observation, with 2,341 never-users with at least one cancer during 388,505 woman-years of observation. Ever-use of oral contraceptives was associated with reduced colorectal (incidence rate ratio [IRR], 0.81; 99% confidence interval [CI], 0.66-0.99), endometrial (IRR, 0.66; 99% CI, 0.48-0.89), ovarian (IRR, 0.67; 99% CI, 0.50-0.89), and lymphatic and hematopoietic cancer (IRR, 0.74; 99% CI, 0.58-0.94).
Findings suggest an increased risk of lung cancer only among ever-users who smoked at recruitment. An increased risk of breast and cervical cancer observed in current and recent users appeared to be lost within about five years of stopping oral contraception, with no evidence of either cancer recurring at increased risk in ever-users with time.1
“There was no evidence of new cancer risks appearing later in life among women who had used oral contraceptives,” the researchers noted. “Thus, the overall balance of cancer risk among past users of oral contraceptives was neutral, with the increased risks counterbalanced by the endometrial, ovarian, and colorectal cancer benefits that persist at least 30 years.”
Length of Observation Key
For Lisa Iversen, PhD, MSc, lead author and research fellow in the Institute of Applied Health Sciences at the University of Aberdeen in Scotland, the breadth of data in the Royal College of General Practitioners’ Oral Contraception Study is a strength of the current analysis.
“Because the study has been going for such a long time, we are able to look at the very long-term effects, if there are any, associated with the Pill,” she noted in a statement accompanying the publication. “What we found from looking at up to 44 years’ worth of data was that having ever used the Pill, women are less likely to get colorectal, endometrial, and ovarian cancer.”
Iversen said researchers also were interested in what the overall balance of all types of cancer is among women who have used the Pill as they enter the later stages of their life. The analysis did not find any evidence of new cancer risks appearing later in life as women age.
“These results from the longest-running study in the world into oral contraceptive use are reassuring,” Iverson said in the statement. “Specifically, pill users don’t have an overall increased risk of cancer over their lifetime, and that the protective effects of some specific cancers last for at least 30 years.”
Add Data to Knowledge Bank
The efficacy of oral contraceptives in ovarian cancer chemoprophylaxis makes them an important strategy for selected high-risk women who have not completed childbearing,2 notes Andrew Kaunitz, MD, University of Florida Research Foundation professor and associate chair of the department of obstetrics and gynecology at the University of Florida College of Medicine-Jacksonville. Also, the finding of a reduced risk of colorectal cancer is consistent with the effect of estrogen-progestin therapy in menopausal women.3
“The finding that long-term, oral contraceptive use does not significantly impact risk of cervical or breast cancer is reassuring for reproductive-age women considering use of combined pills for their contraceptive and/or noncontraceptive benefits,” Kaunitz says.
Robert Hatcher, MD, MPH, professor emeritus of gynecology and obstetrics at Emory University School of Medicine in Atlanta, says he has kept close watch on the past five editions of Clinical Gynecologic Endocrinology and Infertility.4
“There is a new sentence on colorectal cancer in the eighth edition, where one finds the words: ‘Steroid contraception should be offered to women with a strong history of colorectal cancer,’” Hatcher notes. “Protection against colorectal cancer increases the more years a woman has been on combined pills.”
REFERENCES
- Iversen L, Sivasubramaniam S, Lee AJ, et al. Lifetime cancer risk and combined oral contraceptives: The Royal College of General Practitioners’ Oral Contraception Study. Am J Obstet Gynecol 2017; doi: 10.1016/j.ajog.2017.02.002.
- Moorman PG, Havrilesky LJ, Gierisch JM, et al. Oral contraceptives and risk of ovarian cancer and breast cancer among high-risk women: A systematic review and meta-analysis. J Clin Oncol 2013;31:4188-4198.
- Rossouw JE, Anderson GL, Prentice RL, et al; Writing Group for the Women’s Health Initiative Investigators. Risks and benefits of estrogen plus progestin in healthy postmenopausal women: Principal results from the Women’s Health Initiative randomized controlled trial. JAMA 2002;288:321-333.
- Fritz MA, Speroff L. Clinical Gynecologic Endocrinology and Infertility, 8th ed. Philadelphia: Lippincott Williams & Wilkins; 2010.
The latest findings from a long-term study indicate that most women who choose to use oral contraceptives do not expose themselves to long-term cancer harms.
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