Cancer Research Lab

Compared with other anovulatory factors, pregnancy and oral contraceptive are associated with the lowest risk of developing ovarian cancer, according to a report in the January issue of the American Journal of Obstetrics and Gynecology.

The findings suggest that a single definition of years of ovulation may not be suitable for gauging the impact of ovulation on ovarian cancer risk, the authors note.

Dr. Claudio Pelucchi, from Istituto di Richerche Farmacologiche “Mario Negri” in Milan, Italy, and colleagues analyzed data from two case-control studies to determine the impact of various anovulatory factors on ovarian cancer risk. Data from 1822 confirmed cases and 4631 controls were included in the analysis.

Consistent with previous research, as lifetime ovulatory cycles increased, so did the risk of ovarian cancer, the report indicates. For example, compared with women in the lowest quartile of lifetime ovulatory cycles, those in the second, third, and highest quartiles were 60%, 65%, and 81% more likely, respectively, to have ovarian cancer.

One year of anovulation cut the risk of ovarian cancer by 2.5% in general, but the reason for lack of ovulation affected the risk reduction. If the anovulatory year was related to parity, abortion, or oral contraceptive use, the risk fell by 9%, 10%, and 8%, respectively; if the reason was age at menarche or age at menopause, the risk reduction was 1%, and 3%, respectively.

“Parity and oral contraceptive use provided a stronger protective effect than expected for anovulatory action alone,” Dr. Pelucchi and colleagues conclude. “The influence of full-term pregnancy, which implies approximately 1 year of anovulation, was much stronger than that of a year delay of age at menarche or a year anticipation of age at menopause, which indicates that similar anovulation-related factors have different impacts on ovarian cancer risk.”

High numbers of ovulatory cycles combined with a family history of ovarian/breast cancer, raised the risk of ovarian cancer by 3.27-fold, the researchers note.