Abstract
Ovarian cancer is the leading cause of reproductive cancer death in U.S. women. This high mortality rate is due to the lack of early detection methods and ineffectiveness of therapy for advanced disease. Until more effective screening methods and therapies are developed, chemoprevention strategies are warranted. The hen has a high spontaneous prevalence of ovarian cancer and has been used as a model for studying ovarian cancer chemoprevention. In this study, we used the hen to determine the effect of progestin alone, estrogen alone, or progestin and estrogen in combination (as found in oral contraceptives) on ovarian cancer prevalence. We found that treatment with progestin alone and in combination with estrogen decreased the prevalence of ovarian cancer. A significant risk reduction of 91% was observed in the group treated with progestin alone (risk ratio = 0.0909; 95% CI: 0.0117-0.704) and an 81% reduction was observed in the group treated with progestin plus estrogen (risk ratio = 0.1916; 95% CI = 0.043-0.864). Egg production was also significantly reduced in these treatment groups compared with control. We found no effect of progestin, either alone or in combination with estrogen, on apoptosis or proliferation in the ovary, indicating that this is not the likely mechanism responsible for the protective effect of progestin in the hen. Our results support the use of oral contraceptives to prevent ovarian cancer and suggest that ovulation is related to the risk of ovarian cancer in hens and that other factors, such as hormones, more than likely modify this risk.