A meta-analysis published in the October issue of Mayo Clinic Proceedings indicts oral contraceptives as putting premenopausal women at significantly increased risk for breast cancer, especially women who use them prior to having a child.

The meta-analysis builds on many studies with similar findings. But even as the findings stack up, many women are unaware of the risks posed by oral contraceptive use prior to pregnancy, says lead study author Chris Kahlenborn, M.D., of Altoona Hospital in Altoona, Pa.

Dr. Kahlenborn says the discrepancy between risk and patient awareness prompted the meta-analysis, which involved extracting data from 34 studies on whether oral contraceptive (OC) use is associated with premenopausal breast cancer. Included in the studies were women who were premenopausal or younger than 50 and who had been, in most cases, diagnosed with breast cancer during or after 1980.

“As I studied the medical literature, I noticed that a trend appeared,” says Dr. Kahlenborn. “Namely, OC use prior to first-term pregnancy seemed to consistently increase the risk of premenopausal breast cancer. Although the trend was apparent, premenopausal women have continued to hear that OCs are basically safe.”

Rather, patients should know that sustained oral contraceptive use prior to pregnancy increases a premenopausal woman’s risk of developing breast cancer, saysDr. Kahlenborn. He says physicians should better inform their patients of the risks associated with oral contraceptives and calls it a “clear-cut informed consent issue.”

The study noted that 21 out of 23 retrospective studies have shown an increased risk of breast cancer in women who took oral contraceptives prior to pregnancy. It also showed that those women experienced an increased risk of 44 percent.

What’s more, in 2005, the World Health Organization officially classified oral contraceptives as a class one carcinogen, the study’s authors say.

These are staggering results given that more that more than 45,000 women each year develop breast cancer prior to menopause, Dr. Kahlenborn says.

“My hope is that physicians will provide more detailed information to their patients about hormonal contraceptives,” he says. “The authors of our meta-analysis believe that women deserve to be fully informed.”

Other authors of the meta-analysis study are Francesmary Modugno, Ph.D., and Douglas Potter, Ph.D., both of the University of Pittsburgh Cancer Institute, and Walter Severs, Ph.D., of Pennsylvania State University in University Park.

A peer-review journal, Mayo Clinic Proceedings publishes original articles and reviews dealing with clinical and laboratory medicine, clinical research, basic science research and clinical epidemiology. Mayo Clinic Proceedings is published monthly by Mayo Foundation for Medical Education and Research as part of its commitment to the medical education of physicians. The journal has been published for more than 80 years and has a circulation of 130,000 nationally and internationally.