Objective: To examine the influence of hormone-related factors on the risk of invasive epithelial ovarian cancer (ovarian cancer).
Design: Population-based case-control study using in-person interviews.
Setting: Academic department of preventive medicine.
Patient(s): Four hundred seventy-seven ovarian cancer patients and 660 controls.
Intervention(s): None.
Main outcome measure(s): Numbers of and ages at births, oral contraceptive use, and use of menopausal hormone therapy.
Result(s): Compared with nulliparous women, women whose only (last) birth was after age 35 years had an estimated 51% (95% confidence interval: 21%-70%) reduction in risk. If this birth occurred earlier, the reduction in risk was progressively less. Additional (earlier) births reduced the risk further. Oral contraceptive use also reduced risk. Increased body mass index increased risk, but this effect was confined to localized disease and is likely to be a diagnostic bias, as a consequence of other problems associated with being overweight and in itself having no etiological significance.
Conclusion(s): If the major protective effect of a late birth can be confirmed, our most challenging task will be to understand the mechanism to develop a chemoprevention approach to exploit this finding.