Adjuvant radiation (RT) is frequently used in addition to adjuvant chemotherapy (C) for advanced stage endometrial cancer (EC) to improve outcomes, however little data is available to guide the sequencing of adjuvant therapy. We retrospectively reviewed patients with stage III-IVA EC treated at our institution and compared outcomes and toxicities of patients treated with “sandwich” CRT (consisting of C, then RT, then C) versus patients treated with any “other” sequence approach (C then RT, or RT then C, or concurrent CRT). We identified 107 patients with stage III-IVA EC treated at our institution from 2000-2018 who underwent surgical staging followed by both adjuvant C and RT. Only patients with complete treatment records and a minimum of six months follow up were included. Baseline characteristics and details of adjuvant treatment were recorded. Acute and chronic toxicities were defined as side effects < = 6 m and > 6 m after completion of adjuvant CRT, respectively. Toxicity was graded according to CTCAE v4.0. Local (LR), regional (RR), distant (DM), overall (OS), cause specific (CSS), and disease-free survival (DFS) were calculated using Kaplan Meier. Effects of adjuvant treatment order (sandwich vs other) on recurrence, survival, and toxicity were analyzed using t-tests for continuous variables, chi-squared for categorical variables, and Kaplan-Meier estimates. P-values < 0.05 were considered significant. Median age was 63 yrs (33-90) with a median follow up of 3.2 yrs (0.4-14). Histologies were 51% endometrioid, 26% serous, and 23% mixed, other, or unknown. Twenty-one percent were stage IIIA, 9% IIIB, 68% IIIC, and 2% IVA. Twenty-five percent had grade I disease, 27% grade 2, and 43% grade 3. Five yr outcomes were as follows: LR 7%, RR 15%, DM 33%, DFS 82%, and OS 68%. There were no significant differences in clinical outcomes or in the rates of acute toxicity by treatment sequence. Rates of chronic toxicity are shown below. The overall rates of chronic GI, GU, and GYN toxicity were significantly lower in the sandwich group. There were no grade 4 or 5 acute or chronic toxicities. Advanced stage EC is an aggressive disease and adjuvant C and RT are indicated. Clinical outcomes were similar amongst the different sequencing algorithms; however, sandwich therapy led to lower rates of chronic toxicity, offering an opportunity to improved quality of life in survivorship.Tabled 1Abstract 3072; TableToxicity (grade 1, 2, 3)SandwichOtherP-valueOverall26.7%, 15.6%, 0%31.8%, 22.7%, 27.3%<0.001Diarrhea7%, 2%, 0%23%, 0%, 0%0.135Constipation0%, 0%, 0%14%, 0%, 0%0.032Small bowel/colon obstruction0%, 0%, 0%4.5%, 0%, 0%0.328Urinary tract pain/dysuria0%, 0%, 0%13.5%, 4.5%, 0%0.013Frequency/Urgency7%, 0%, 0%23%, 4%, 0%0.051Pelvic pain0%, 0%, 0%27%, 0%, 0%0.001Vaginal Stenosis/Stricture9%, 9%, 0%27%, 14%, 18%0.001 Open table in a new tab