The effect of maintenance hormone therapy on overall survival in advanced-stage low-grade serous ovarian carcinoma: A risk-set matched retrospective study

5568 Background: Low-grade serous ovarian carcinoma (LGSOC) is a rare malignancy often treated similarly to high-grade serous ovarian carcinoma (HGSOC) despite differences in clinical behavior and carcinogenesis. Observational studies suggest that, among patient with advanced-stage LGSOC, maintenance hormonal therapy (HT) following primary treatment is associated with improved progression free survival. We conducted a multi-institutional observational study to investigate whether HT is associated with an overall survival advantage in this setting. Methods: We included patients with histologically confirmed stage III or IV LGSOC diagnosed between Jan 1, 2004, and Dec 31, 2019, treated in Commission on Cancer accredited cancer programs in the US. Patients who received HT within 6 months of diagnosis were matched to controls who did not initiate HT during this timeframe. The primary outcome was risk of death from any cause, within five-years of initiation of HT or observation. For each treated patient, we employed risk-set propensity score matching to identify a control in a manner that avoided the introduction of immortal-time-bias, and balanced groups with respect to year of diagnosis, upfront treatment strategy, age, stage, race/ethnicity, comorbidity index, insurance status, zip-code median income, and cancer program type. Results: There were 296 patients who initiated HT within 6 months of diagnosis, and 2,805 potential controls. Patients who received HT were more often treated in academic medical centers (55% vs 44%), diagnosed later in the study period (62% vs 23% diagnosed in 2018-2019), and received upfront chemotherapy less frequently (55% vs 83%). After risk set and propensity score matching, we identified 204 patients treated with HT and 204 untreated controls, who were otherwise similar with respect to measured covariates. In the matched cohort, maintenance HT was associated with a reduction in the risk of death (hazard ratio 0.61; 95% CI 0.37-0.99), corresponding to a 60-month survival of 71% compared with 61%, and an improvement in 5-year life expectancy of 3.6 months (95% CI 0.004-7.2). Conclusions: Maintenance hormone therapy following primary management of LGSOC is associated with an overall survival benefit compared with observation.