What You Need to Know
- Recent use of some oral contraceptives is associated with an increased risk of breast cancer.
- Risk varies with formulation of the contraceptives, and those with low-dose estrogen were not associated with cancer.
The Study: In a nested case-control study, women (ages 20-49) who had used birth control pills within the previous year had a 1.5x increase in the risk of disease, compared with those who had never or formerly used the drugs, according to Elisabeth Beaber, PhD, of the Fred Hutchinson Cancer Research Center in Seattle, and colleagues.
But the risk varied with formulation of the contraceptives; some types — notably those with low-dose estrogen — were not associated with cancer, Beaber and colleagues reported in the Aug. 1 issue of Cancer Research.
Many women ask about oral contraceptives and breast cancer,” and the benefits and risks need to be clearly understood, commented Holly Pederson, MD, of the Cleveland Clinic.
In women under 50, she told MedPage Today, “their absolute risk of breast cancer is less than 2%.”
But while that risk “raises red flags,” the main concern is not oral contraceptives, she said, but familial and genetic predispositions, such as mutations in the BRCA genes. Those factors, she noted, were not analyzed in the study.
Pederson added that it’s “important to reinforce to our patients that the most commonly used birth control pill — low-dose [estrogen] monophasic — was even in this study not associated with an increased risk.”
The issue is not a new one, Beaber and colleagues noted: a 1996 pooled analysis of more than 150,000 women, a third of them with breast cancer, showed a slight increase in risk associated with oral contraceptives.
Since then, two major studies have reached differing conclusions. The Nurses’ Health Study II found an excess breast cancer risk associated with current oral contraceptive use and with one specific formulation, while the Women’s Contraceptive and Reproductive Experiences Study found no such risks.
But most such studies have relied on participant recall, lacked data on current contraceptive formulations, and didn’t stratify breast cancer risk by estrogen receptor status, they noted.
To help fill the gap, Beaber and colleagues turned to the records of the Group Health Cooperative, an integrated health care delivery system in the Seattle-Puget Sound area.
They obtained information on estrogen receptor status from the Surveillance, Epidemiology, and End Results (SEER) database.
Other findings related to recent use of oral contraceptives included:
- High-dose estrogen was associated with an odds ratio for cancer of 2.7
- Ethynodiol diacetate was associated with an odds ratio of 2.
- Triphasic dosing with an average of 0.75 milligrams of norethindrone was associated with an odds ratio of 3.1
- Other types, including low-dose estrogen oral contraceptives, were not linked to an increased risk, they reported.
The odds ratio for estrogen receptor–positive disease was 1.7 (with a 95% confidence interval from 1.3 to 2.1), while for estrogen receptor-negative disease it was 1.2, with a 95% confidence interval from 0.8 to 1.8. The difference between the two was not significantly different, Beaber and colleagues reported.
“Our results suggest that use of contemporary oral contraceptives in the past year is associated with an increased breast cancer risk relative to never or former oral contraceptive use,” Beaber said in a statement, adding the risk “may vary by oral contraceptive formulation.”
Beaber cautioned that the results need confirmation and “should be interpreted cautiously.” She noted that breast cancer remains rare in young women and that oral contraceptives have “numerous established health benefits” that need to be considered as well by doctors and patients.
Those benefits include reproductive planning, menses regulation, decreased dysmenorrhea, and decreased risk of benign breast conditions, she and colleagues concluded.
My Take: Fortunately, the overall risk of breast cancer is quite low in this age group, so even though a 1.5x increase seems extraordinarily large (and I would note that the study numbers are remarkably low (at least for women on the pill for over 6 months), it represents only a small increase in absolute risk. And remember, low-dose estrogen pills were not associated with increased risk. I do think that those with a strong family history of breast cancer may wish to proceed with more caution. I’m Dr. Michael Hunter.
The small print: The material presented herein is informational only, and is not designed to provide specific guidance for an individual. Please check with a valued health care provider with any questions or concerns. As for me, I am a Harvard- , Yale- and UPenn-educated radiation oncologist, and I practice in the Seattle, WA (USA) area. I feel genuinely privileged to be able to share with you. If you enjoyed today’s offering, please consider clicking the follow button at the bottom of this page.
Available now: Understand Colon Cancer in 60 Minutes; Understand Brain Glioma in 60 Minutes. Both can be found at the Apple Ibooks store. Coming Soon for iPad: Understand Breast Cancer in 60 Minutes; Understand Colon Cancer in 60 Minute; Understand Colon Cancer in 60 Minutes; Understand Brain Glioma in 60 Minutes. Thank you.
Primary reference: Beaber E, et al “Recent oral contraceptive use by formulation and Breast cancer risk among women 20 to 49 years of age” Cancer Res 2014; 74; 4078–89.
Secondary reference: http://www.medpagetoday.com/HematologyOncology/BreastCancer/47024