Past studies have examined oral contraceptives and breast cancer risk and have indicated that recent use slightly increases the risk for breast cancer however, most studies on the usage of oral contraceptives were self-reported and did not examine contemporary oral contraceptive formulations.
In a new study Dr. Elisabeth Beaber, PhD, of the Fred Hutchinson Cancer Researcher Center in Seattle and colleagues conducted a nested case- control study included 1,102 women, aged 20 to 49 years and was diagnosed with invasive breast cancer from 1990 to 2009 and 21,952 controls matched to cases on age, year, enrollment length, and medical chart availability.
Detailed oral contraceptive use information was ascertained from electronic pharmacy records. Researchers classified the contraceptives according to combinations; estrogen and progestin components, doses, and monophasic or triphasic dosing schedule.
Estrogen receptor status had come from the Surveillance, Epidemiology, and End Results (SEER) database.
The results showed that women who had used oral contraceptives within the previous year had a 50% increase for breast cancer risk compared to those who never used or had previously used oral contraceptives.
They also found recent use of oral contraceptives with high dose estrogen had an odds ratio of 2.7, ethynodiol diacetate (brand name Zovia) had an odds ratio of 2.6 and triphasic dosing with an average of 0.75 milligrams of norethindrone was associated with an odds ratio of 3.1.
Other types of contraceptives including low-dose estrogen were not associated to an increased risk of breast cancer.
In their conclusion the researchers write “Our results suggest that recent use of contemporary oral contraceptives is associated with an increased breast cancer risk, which may vary by formulation. If confirmed, consideration of the breast cancer risk associated with different oral contraceptive types could impact discussions weighing recognized health benefits and potential risks.”
Dr. Beaber cautions that their results need confirmation and "should be interpreted cautiously."
Dr. Beaber noted that in young women breast cancer is rare and oral contraceptives have "numerous established health benefits" that need to be considered as well by doctors and patients.
The researchers concluded that those benefits include reproductive planning, menses regulation, decreased dysmenorrhea, and decreased risk of benign breast conditions
This study is published in Cancer Research.