Stage IC grade 1 endometrioid adenocarcinoma of the ovary: assessment of post-operative chemotherapy de-escalation.

Objective: Given limited real-world practice data evaluating the National Comprehensive Cancer Network clinical practice guidelines for possible post-operative chemotherapy omission as a treatment option for patients with stage IC grade 1 endometrioid ovarian carcinoma, this population-based study examined the association between post-operative chemotherapy and overall survival in this tumor group.

Methods: The National Cancer Institute's Surveillance, Epidemiology, and End Results program was retrospectively queried. The study population was 1207 patients with stage IC grade 1-3 endometrioid ovarian carcinoma who received primary cancer-directed surgery from 2007 to 2020. Overall survival was assessed with multivariable Cox proportional hazard regression model.

Results: The median age was 52, 54, and 55 years for grade 1, 2, and 3 groups, respectively (p=0.02). Grade 1 and 2 tumors were more common than grade 3 tumors (n=508 (42.1%), n=493 (40.8%), and n=206 (17.1%), respectively). Chemotherapy use rate for grade 1 tumors was lower compared with grade 2-3 tumors (67.9%, 76.5%, and 78.6%, respectively, p<0.001). When nodal evaluation was performed for grade 1 tumors, among patients who did not receive post-operative chemotherapy and among those who did, 5-year overall survival rate exceeded 90% (93.3% and 96.0%, respectively), with statistically non-significant hazard estimates (adjusted hazard ratio (aHR) 1.54, 95% CI 0.63 to 3.73). In contrast, post-operative chemotherapy omission for patients who did not undergo nodal evaluation was associated with decreased overall survival (5-year rates 82.3% vs 96.0%, aHR 5.41, 95% CI 1.95 to 15.06). Results were similar for node-evaluated grade 2 tumors (5-year overall survival rates, 94.6% and 94.4% for node-evaluated post-operative chemotherapy omission and administration, respectively), but not in grade 3 tumors.

Conclusion: The results of this population-based study may partially support the current clinical practice guidelines for post-operative chemotherapy omission as a possible option for patients with stage IC grade 1 endometrioid adenocarcinoma of the ovary for those who had lymph node evaluation. Observed data were also supportive for node-evaluated grade 2 tumors, warranting further evaluation.