Abstract B24: Personal history of endometriosis and survival in ovarian cancer patients: A pooled analysis of 10 studies from the Ovarian Cancer Association Consortium.

Background: There is mounting evidence that a personal history of endometriosis is associated with an increased risk of ovarian cancer. Previous studies have shown that ovarian cancer patients with a prior diagnosis of endometriosis had more favorable outcomes than women without this condition, likely due to increased surveillance resulting in earlier detection. However, most of these studies were relatively small in size and did not consider histological subtypes in their analyses. Given the increased recognition of the importance of histology in ovarian cancer prognosis, we examined the association between history of endometriosis and overall survival among women diagnosed with ovarian cancer in a large multi-national sample. Methods: We utilized data from 10 case-control studies participating in Ovarian Cancer Association Consortium and used age- and stage-adjusted Cox- proportional hazards models to estimate associations between history of endometriosis and overall survival among patients diagnosed with invasive epithelial ovarian carcinoma. Analyses were also conducted separately for histological subtypes of ovarian cancer (low grade serous, high grade serous, mucinous, endometriod and clear cell). We also examined the associations within strata of menopausal status and body mass index (BMI) categories. Results: A personal history of endometriosis was inversely associated with risk of death (hazard ratio (HR)=0.84; 95% confidence interval (CI) 0.74-0.95) among all ovarian cancer patients (n=7033). We observed strong risk reductions among patients with low-grade serous disease (n=214; HR=0.48; 95% CI 0.24-0.95), but not among patients with high-grade serous tumors (n=3273; HR=0.97; 95% CI 0.83-1.14). Furthermore, patients with clear cell tumors (n=555) had a 40% risk reduction (HR=0.60; 95% CI 0.39-0.91). No significant associations were observed for patients with mucinous (n=356) or endometriod (n=1072) ovarian cancer, although the HRs were well below the null value (HR=0.82; 95% CI 0.33-1.05, and HR=0.70; 95% CI 0.47-1.05, respectively). When we considered BMI as a potential effect modifier, we observed that the survival benefit associated with a personal history of endometriosis was restricted to normal weight women (HR=0.70; 95% CI 0.58-0.85) and absent among overweight (HR=1.02; 95% CI 0.82-1.28) and obese (HR=1.08; 95% CI 0.82-1.40) patients. The relationship between a personal history of endometriosis and ovarian cancer outcomes did not differ between premenopausal and postmenopausal patients. Conclusion: Our results suggest that history of endometriosis is associated with overall survival among women diagnosed with invasive ovarian cancer, particularly among clear cell and low grade serous carcinomas, including after control for stage of disease. Despite being underpowered to adequately assess between endometriosis and outcomes for patients with mucinous and endometrioid tumors, there was a trend towards improved survival for those with a personal history of endometriosis. These findings underscore the importance of examining prognostic indicators for ovarian cancer among distinct histological subgroups, as well as to distinguish between low-grade serous and high-grade serous disease. Moreover, the constellation of changes caused by endometriosis to induce ovarian cancer may alter the tumor microenvironment and change the ultimate disease prognosis. Future studies are needed to determine the role of endometriosis in the tumor environment and ovarian cancer prognosis. Citation Format: Albina N. Minlikeeva, Jo L. Freudenheim, C. Leigh Pearce, J.Brian Szender, Ovarian Cancer Association Consortium, Kirsten B. Moysich. Personal history of endometriosis and survival in ovarian cancer patients: A pooled analysis of 10 studies from the Ovarian Cancer Association Consortium. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr B24.