(PQA3) Why is Ovarian Cancer Primarily a Disease of Postmenopausal Women



 DESCRIPTION (provided by applicant): Epithelial ovarian cancer is predominantly a disease of postmenopausal women, with 80-90% of ovarian cancer cases occurring after the age of 40. The peak incidence of menopause occurs at age 51, while the peak incidence of invasive epithelial ovarian cancer occurs at age 63. Many theories of postmenopausal onset of ovarian cancer have been proposed, including incessant ovulation and inflammation, hormonal changes, reduced immunity, increased cell senescence and uncontrolled production of reactive oxygen species. A poor understanding of the initiating events in ovarian cancer has significantly hampered our efforts towards early ovarian cancer detection and prevention. It is increasingly accepted that ovarian cancer actually originates in the fallopian tube with malignant cells shedding to the adjacent ovary. Since the bulk of the tumor typically forms in the ovary, rather than the fallopian tube, ovaries must play a significant role in the early stages of cancer development. Epidemiologic data consistently show that ovarian cancer risk increases with the number of ovulatory cycles, indicating that ovulation plays a role in ovarian cancer etiology. However, it is paradoxical that women typically develop ovarian cancer more than a decade after their last ovulation. During the postmenopausal years, the ovarian follicles are depleted and much of the remaining ovary is remodeled to form fibrotic scar tissue. In contrast to the current view of the atrophic ovary as a nonfunctional fibrotic scar, we postulate that the collagen-rich microenvironment of the postmenopausal ovary provides fertile soil for the seeding of neoplastic tubal cells. This hypothesis is based on the recognized role of fibrosis and collagen remodeling in facilitating tumorigenesis in several cancer types and on our recent finding that similar sets of collagen- remodeling genes are enriched during ovarian cancer progression and ovarian follicle regression. To test our hypothesis, we will first identify which molecular events are associated with human ovarian aging and menopausal status (Aim 1) and then test in a mouse model whether ovarian aging and/or fibrosis contribute to increased implantation of tubal cells into the ovary (Aim 2). Proof of our hypothesis will re-shape the current paradigms about ovarian cancer etiology. Moreover, determining which cellular and molecular processes promote and inhibit implantation of cancer cells into the ovary will provide needed insight into the identiy of targets for prevention and early detection.