The use of contraceptive pills has been associated with an increased risk of breast cancer, according to a report in the American Journal of Epidemiology.

Until now, the reported association between breast cancer and oral contraceptives was based “largely on…studies conducted before 1990,” according to Dr. Lynn Rosenberg, from Boston University, and colleagues.

Using data from the Case-Control Surveillance Study the authors determined whether contraceptive pill use was associated with increased breast cancer risk in women diagnosed between 1993 and 2007, and if so, whether the association differed by race or the hormone receptors found on the breast cancer.

The study involved 907 women with breast cancer and 1711 without breast cancer.

Women who used oral contraceptives for 1 year or longer were 50 percent more likely to have breast cancer than those who used them for less time or not at all.

There was evidence that a longer duration of use, black ethnicity, and use within the last 10 years increased the odds of breast cancer, although all of these associations may have just occurred by chance. The hormone receptor status did not affect the association between contraceptive use and breast cancer.

“Given the widespread use of oral contraceptives, continued evaluation of their possible health effects may be warranted,” Rosenberg and colleagues conclude.

SOURCE: American Journal of Epidemiology, February 15, 2009.