August 20, 2014
Breast Cancer Risk Increased by Specific Birth Control
Pill Types

Seattle—Recent use of birth control pills can increase breast cancer risk, but only when high-dose estrogen and a few other formulations were involved, according to a new study.

That information was reported recently in Cancer Research, a journal of the American Association for Cancer Research.

“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, and that this risk may vary by oral contraceptive formulation,” explained Elisabeth F. Beaber, PhD, MPH, a staff scientist in the Public Health Sciences Division of Fred Hutchinson Cancer Research Center in Seattle.

“Our results require confirmation and should be interpreted cautiously,” warned Beaber. “Breast cancer is rare among young women, and there are numerous established health benefits associated with oral contraceptive use that must be considered. In addition, prior studies suggest that the increased risk associated with recent oral contraceptive use declines after stopping oral contraceptives.”

For the nested case-control study, the researchers focused on 1,102 women in the Group Health Cooperative in the Seattle-Puget Sound area diagnosed with breast cancer between 1990 and 2009, comparing them to 21,952 controls. Unlike previous studies that relied on self-reporting, electronic pharmacy records were used to gather detailed information on oral contraceptive use including drug name, dosage, and duration of medication.

Results indicate that recent oral contraceptive use increased breast cancer risk overall by 50%, compared with never or former use, but the risk varied significantly by pill formulation.

The study found that birth control pills containing high-dose estrogen increased breast cancer risk 2.7-fold, and those containing moderate-dose estrogen increased the risk 1.6-fold. In addition, pills containing ethynodiol diacetate increased the risk 2.6-fold, and triphasic combination pills containing an average of 0.75 milligrams of norethindrone increased the risk 3.1-fold.

Birth control pills containing low-dose estrogen did not increase breast cancer risk, however.

Fewer than 1% of study controls who were recent oral contraceptives users filled at least one prescription in the past year for high-estrogen dose oral contraceptives, compared to about 24% for low dose and 78% for moderate dose, Beaber noted.

“If confirmed, consideration of the breast cancer risk associated with different oral contraceptive types could impact discussions weighing recognized health benefits and potential risks,” the authors write.

U.S. Pharmacist Social Connect