Women who recently used certain birth control pills that contain a high level of estrogen were at an increased risk for developing breast cancer, compared to women who did not use such contraceptives.

According to the American Cancer Society, approximately one in eight (12 percent) American women will develop invasive breast cancer during their lifetime.

The new study involved 1,102 women diagnosed with breast cancer and 21,952 control participants. Researchers discovered that recent use of oral contraceptives increased the chance of developing breast cancer by as much as 50 percent, compared to those who have either never used contraceptives, or have not used them recently.

Birth control pills that contain low levels of estrogen did not appear to have an effect on the risk of breast cancer.

Elisabeth F. Beaber, PhD, MPH, a staff scientist in the Public Health Sciences Division of Fred Hutchinson Cancer Research Center in Seattle, Washington, believes further investigation is warranted to confirm the results of the study, and recommends that healthcare providers should interpret the findings with a high degree of caution.

“Our results suggest that use of contemporary oral contraceptives [birth control pills] 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,” said Beaber in a statement.

The findings of the study are published in Cancer Research, a journal of the American Association for Cancer Research.