Ovarian cysts do not increase the risk of breast cancer, according to the results of a review study. In fact, such cysts were associated with a 30-percent decreased risk of breast cancer, the investigators report.

Non-cancerous or “benign” ovarian cysts are associated with infertility and menstrual cycle irregularities, Dr. Cristina Bosetti and colleagues explain in their report, published in the International Journal of Cancer. On that basis, it has been suggested that ovarian cysts may alter hormone levels that in turn could influence breast cancer risk.

Individual studies have failed to either support or refute that theory. Therefore, Bosetti, from Instituto di Ricerche Farmarmacologiche Mario Negri in Milan, Italy, and her team combined data from two hospital-based studies conducted in Italy between 1983 and 1991 and between 1991 and 2001, as well as one performed between 1992 and 2001 in Switzerland.

The researchers included in their analysis 6315 breast cancer patients and 6315 comparison subjects admitted to the same hospitals for unrelated reasons. The subjects had been interviewed while hospitalized regarding demographic, menstrual and reproductive factors, including a history of ovarian cysts.

Five percent of breast cancer patients and 7 percent of comparison subjects reported a history of ovarian cysts, Bosetti and her associates report. This translates into a 28 percent reduced risk of breast cancer in subjects with ovarian cysts.

The association between ovarian cysts and reduced breast cancer risk was strongest among women with irregular menstrual cycles, those who had never used oral contraceptives, those who undergone ovary removal or hysterectomy, and those with lower body weights.

These findings prompted the investigators’ to conclude that “although some hormonal correlates of ovarian cysts may have a role on breast cancer risk, a biological explanation of this association is still unclear.”

SOURCE: International Journal of Cancer, October 2006.