As the optimal adjuvant management of stage IA serous or clear cell endometrial cancer is controversial, a multi-institutional review was conducted with the objective of evaluating the appropriateness of various strategies including observation.

Retrospective chart reviews for 414 consecutive patients who underwent hysterectomy for FIGO stage IA endometrial cancer with serous, clear cell or mixed histology between 2004 and 2015 were conducted in 6 North American centers. Time-to-event outcomes were analyzed by Kaplan-Meier estimates, log-rank test, univariable and multivariable cox proportional hazard regression models.

Post-operative management included observation (50%), chemotherapy and radiotherapy (RT) (27%), RT only (16%) and chemotherapy only (7%). The 178 RT patients received external beam (EBRT, 16%), vaginal vault brachytherapy (VVB, 56%) or both (28%). Among patients without any adjuvant treatment, 5-year local control (LC), disease free survival (DFS) and cancer-specific survival (CSS) were 82% (95% confidence interval: 74-88), 70% (62-78) and 90% (82-94), respectively. CSS in patients without adjuvant treatment was improved with adequate surgical staging (100% vs. 87% (77-92), log-rank p=0.022). Adjuvant VVB was associated with improved LC (5-year 96% (91-99) vs. 84% (76-89), log-rank p=0.007) and DFS (5-year 79% (66-88) vs. 71% (63-77), log-rank p=0.033). Adjuvant chemotherapy was associated with better LC (5-year 96% (90-98) vs. 84% (77-89), log-rank p=0.014) and DFS (5-year 84% (74-91) vs. 69% (61-76), log-rank p=0.009). On multivariable analysis, adjuvant chemotherapy and VVB were associated with improved LC while adjuvant chemotherapy and age were significant for DFS.

In stage IA serous or clear cell uterine cancer, adjuvant RT and chemotherapy were associated with better LC and DFS. Observation may be appropriate in patients who have had adequate surgical staging.