Oral contraceptive use does not increase long-term cancer risk

Women who used oral contraceptives did not demonstrate increased long-term cancer risk, according to results of the Royal College of General Practitioner’s Oral Contraception Study.

In fact, many women demonstrated reduced risk for certain malignancies, and this benefit persisted for several years after oral contraceptive use ended.

Lisa Iversen, PhD, research fellow at Institute of Applied Health Sciences at University of Aberdeen in the United Kingdom, and colleagues assessed long-term cancer risks and benefits associated with combined oral contraceptive use among 46,022 women recruited to the Royal College of General Practitioner’s Oral Contraception Study between 1968 and 1969.

Researchers followed study participants for up to 44 years.

Ever use of oral contraceptives appeared associated with decreased risk for colorectal cancer (incidence rate ratio [IRR] = 0.81; 99% CI, 0.66-0.99), endometrial cancer (IRR = 0.66; 99% CI, 0.48-0.89), ovarian cancer (IRR = 0.67; 99% CI, 0.5-0.89), and lymphatic and hematopoietic cancer (IRR = 0.74; 99% CI, 0.58-0.94).

Researchers observed increased risks for breast and cervical cancers among current and recent oral contraceptive users, but the increased risks dissipated within approximately 5 years of contraceptive use cessation. Results also showed an increased risk for lung cancer among contraceptive ever users who reported smoking at study enrollment.

HemOnc Today spoke with Iversen about the study results, their potential implications, and how the data compare with previous research into the association between contraceptive use and cancer risk.

Question: What prompted this study?

Answer: Our study is the longest running of its kind in the world. It is an ongoing cohort study established in 1968 with the aim of investigating the health effects of oral contraceptives.

Q: What did you find?

A: Our study, which has followed 46,000 women in the United Kingdom for up to 44 years, has shown that the protective benefits of reductions in endometrial, ovarian and colorectal cancers in women who used oral contraceptives during their reproductive years lasted for at least 30 years after they stopped. We did not find any evidence of new cancer risks appearing later in life among women who had used oral contraceptives.

Q: Did the findings surprise you?

A: The reductions in the risk for endometrial, ovarian and colorectal cancer associated with use of oral contraceptives have previously been reported. However, due to the longevity of our study, we have been able to demonstrate that these reductions in cancer risk are persistent, lasting at least 30 years after women stopped taking oral contraceptives.

Q: What are the potential implications of the findings?

A: We believe our findings are reassuring for women. Most women who chose oral contraception did not expose themselves to long-term cancer harms. Instead, with some cancers, many women benefitted from important reductions in risks that persist for many years after stopping.

Q: How do these findings coincide with previous literature on the association between contraceptive use and cancer risk?

A: Our findings are consistent with previous reports, but they are novel in that we have been able to examine the very long-term effects of oral contraceptives on cancer risk. Our results demonstrate persistent reductions in the risk for endometrial cancer, ovarian cancer and colorectal cancer, which remain many years after women stop using oral contraceptives.

Q: Is this issue settled, or do questions remain unanswered?

A: The women in our study primarily used older types of combined oral contraceptives containing 50 micrograms of estrogen combined with an older progestogen that might not reflect the experience of today’s users of oral contraceptives. Limited evidence suggests that oral contraceptives used by women today are likely to have similar effects, but this has not yet been confirmed.

Q: What might future research entail?

A: Future research might consider the cancer risks associated with contemporary oral contraception and other types of hormonal contraception.

Q: Is there anything else th at you would like to mention?

A: Our study has considered the association between oral contraception and subsequent cancer diagnosis, and most women who have used oral contraception do not expose themselves to long-term cancer harm. A different question is whether oral contraception use affects prognosis after cancer diagnosis, which our study did not evaluate. – by Jennifer Southall

Reference:

Iversen L, et al. Am J Obstet Gynecol. 2017;doi:10.1016/j.ajog.2017.02.002.

For more information:

Lisa Iversen, PhD, can be reached at Institute of Applied Health Sciences, University of Aberdeen, West Block, Room 1:128, Polwarth Building, Foresterhill, Aberdeen, AB25 2ZD; email: lliversen@abdn.ac.uk.

Disclosure: Iversen reports no relevant financial disclosures.