by Matt Rosenberg March 5th, 2012
Delving into a hot-button topic about which they state all the science is distinctly not settled, a female-led team of researchers and doctors from the University of Washington in Seattle and the Seattle-based Group Health Cooperative HMO – in preliminary findings of a new study – report that for women aged 20 to 49, use of certain types of oral contraceptives within the previous year are “associated with particularly elevated risk” of being diagnosed with invasive breast cancer. The abstract-only findings were published online in mid-February in the journal Cancer Epidemiology, Biomarkers and Prevention (link, screen shot.) The findings are also highlighted by Group Health at their Web site in a brief titled, “Taking newer birth control pills may be linked to a higher risk of breast cancer.”
The lead author, Elisabeth Beaber, a UW PhD candidate in epidemiology, declined to discuss the published first-stage research outcomes prior to further peer review. Meanwhile, Beaber was scheduled to give a presentation on the current report March 6 at the 2012 annual meeting of the American Society of Preventive Oncology in Washington D.C. as part of a session (referenced in the meeting agenda on p. 12) titled “Breast Cancer: Risk Prediction, Screening and Behavior Modification.”
The preliminary results of the study show that for women age 20 to 49, using within the last year an oral contraceptive formulation with high-dose estrogen or a progestin called ethynodial diacetate raises the odds ratios to 2.7 and 2.6, respectively, of being diagnosed with invasive breast cancer within that time frame – compared to women who do not use those formulations. An odds ratio of 1 represents no association.
Odds ratios are used to convey the relative risk of an association between two factors; they don’t prove a strict cause-and-effect relationship. In the same study, a lower odds ratio of being diagnosed with breast cancer, 1.2, was found for women 20-49 who in the last year took a different kind of oral contraceptive, formulated with progestin norgestimate. With a fourth type of oral contraceptive formulation, low dose estrogen, researchers found an odds ratio of 1, or no association with breast cancer.
But overall, the researchers report, oral contraceptive use by women age 20-49 was associated with a 60 percent increased risk of diagnosis, within a year, of invasive breast cancer.
The authors conclude:
These results suggest that recent use of contemporary (oral contraceptive) formulations is associated with an elevated risk of breast cancer among women ages 20-49, with associations varying somewhat by (oral contraceptive) formulation. Although breast cancer is rare among young women, the potential risk of breast cancer associated with certain formulations could impact (oral contraceptive) recommendations by providers if these findings are confirmed.
Electronic pharmacy records used in study, not self-reports
The authors state their inquiry is necessary because the bulk of past studies demonstrating a “modest increased risk” in breast cancer for younger women who’ve recently used oral contraceptives, “have relied on self-reported use and have not characterized risks associated with newer (oral contraceptive) formulations.”
Their so-called “nested case-control study” corrects those shortcomings, they write. The researchers used data on 1,102 women enrollees age 20-49 at the Group Health Cooperative HMO serving greater Seattle who were diagnosed with invasive breast cancer from 1990 to 2009, compared to almost 22,000 randomly selected control subjects who were also Group Health enrollees. The information on type of oral contraceptives used, plus dose and duration, was mined not – as in the past – from self-reports, but rather, from electronic pharmacy records.
The authors also state numerous other factors that could influence study outcomes were factored into the analysis as part of their “multivariate-adjusted conditional logistic regression” to help shape their preliminary findings.
Broader study eyed
In a grant application to the National Cancer Institute to help fund the study, co-author Dr. Diana Buist of the Group Health Research Institute, and one of Beaber’s PhD advisors, states that this pilot study “will provide vital preliminary data for a potential multistate study” within the 14-HMO Cancer Research Network.
In addition to Beaber and Buist, co-authors of the current study include William E. Barlow, Senior Investigator at the Group Health Research Institute; plus Dr. Christopher I. Li and Dr. Kathleen E. Malone, both of the UW and the Fred Hutchinson Cancer Research Institute, and Dr. Susan D. Reed of UW.