Birth control pills containing high doses of estrogen and a few other formulations may increase the risk of breast cancer in women younger than 50, according to a recent study.

Researchers 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, HealthDay reported.

"There are numerous oral contraceptive formulations," Elisabeth Beaber, lead researcher and a staff scientist at the Fred Hutchinson Cancer Research Center in Seattle, told HealthDay. "Some of these formulations increase breast cancer risk while other formulations do not raise risk."

For the study, researchers collected data from more than 1,000 women diagnosed with breast cancer and nearly 22,000 controls.

They found that recent oral contraceptive use increased breast cancer risk by 50 percent, compared with never or former use. All study participants were at Group Health Cooperative in the Seattle-Puget Sound area. Patients received a cancer diagnosis between 1990 and 2009.

"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," Beaber said in a statement. "Our results require confirmation and should be interpreted cautiously."

Beaber warned that the study should be interpreted cautiously.

"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," she said.

The findings were recently published in the journal Cancer Research.