Background. The ovarian cancer incidence rate is higher for women over 55 years of age than for younger women, but it increases less rapidly with age after age 55 years than before. This slower rate of increase suggests that the postmenopausal ovary may be less exposed or less susceptible than the functioning one to endogenous or exogenous carcinogens. For example, it is not exposed to mitotic stimuli at follicle rupture, which may increase the likelihood of malignancy.
Methods. Findings from a collaborative analysis of 12 U.S. case–control studies are used to examine associations between invasive epithelial ovarian cancer and certain reproductive and hormonal characteristics, and to determine if those associations change as women age.
Results. Ovarian cancer risk reductions were associated with pregnancy (regardless of outcome), lactation, and oral contraceptive use. The percentage risk reduction associated with pregnancy was smaller for older women than younger women, although the absolute magnitude of the risk reduction increased with age. In contrast, the percentage risk reduction associated with oral contraceptive use was greater for older women. The total duration of ovulation was strongly associated with increased risk in women under 55 years of age, but not in older women.
Conclusions. The greater protection to older women associated with oral contraceptive use suggests that the early high-potency contraceptive formulations used by these women may have been more protective than recent ones. The sparsity of strong risk factors in older women emphasizes the need for sensitive and specific markers for early detection of ovarian malignancy in this age group.