Introduction/Background Endometriosis affects approximately 10% of women of reproductive age globally. There is evidence for an anatomical distribution of benign adnexal masses with endometriotic lesions exhibiting a left lateral predisposition. Endometriosis is associated with a 1.9-fold greater risk of ovarian cancer, specifically endometrioid (2.3-fold) and clear cell (3.4-fold) types. The primary aim of this study is to determine whether a left lateral predisposition of ovarian CCC and EC exists.

Methodology A retrospective cohort study of all patients diagnosed with EC and CCC in Northern Ireland (NI) between March 2011 and June 2018. Data was collected electronically. ANOVA was used to analyse preoperative prediction of stage, chi-squared (χ2) was used to compare left- and right-sided masses. Survival was estimated using Kaplan-Meier and log-rank test. A p-value <0.05 was considered statistically significant.

Results 158 patients were identified (95 EC, 55 CCC, 8 mixed). Mean age was 57.65 years with 69% presenting at stage 1. The mean CA125 was 559 U/mL (p = 0.850) and mean abdominal mass size was 14.12cm (p = 0.732). The most common presenting symptom was an abdominal mass (37%). Despite 67% of patients having endometriosis on final pathology, only 8.9% had a known history pre-operatively. 51% of tumours were located on the left (p = 0.036) and when analysed separately this was significant for EC (P = 0.002) but not for CCC (P = 0.555). The 1-, 3- and 5-year median overall survival for all types/stages was 85%, 78% and 71% respectively.

Conclusion While CCC and EC are associated with endometriosis, only EC exhibits a left lateral predisposition. There is no association between preoperative CA125 or abdominal mass size and stage of disease.

Disclosures None declared.