What are the Optimal Radiation Fields for FIGO IIIC Endometrial Cancer? A Multi-Institutional Study

Abstract

In GOG-258, rates of pelvic & para-aortic (PA) nodal failure were lower with the addition of adjuvant radiation (RT) compared to chemotherapy alone, although details on RT fields have not yet been reported. In patients with node positive endometrial cancer, the selection of pelvic (PRT) vs. extended field RT (EFRT) has yet to be defined. This study evaluates outcomes and sites of failure in patients with FIGO stage IIIC endometrial cancer treated with PRT vs. EFRT. In a multi-institutional retrospective cohort study, we identified 143 patients with FIGO IIIC endometrioid endometrial cancer s/p surgical staging who received adjuvant RT from 1/2000-12/2016. RT fields were reviewed and categorized as EFRT if the superior field border included the renal hilum or PRT if below. Baseline characteristics & outcomes were compared by stage (IIIC1 vs. IIIC2) and RT type (PRT vs. EFRT). Actuarial estimates of RFS & OS were calculated by Kaplan-Meier & compared by logrank. Sites of failure were reported as local (vaginal), regional (pelvic or PA nodal) or distant, & within or outside the RT field. Median follow-up was 59.3 months. Clinical and treatment characteristics for 3 treatments groups are described in Table 1: pelvic node positive (IIIC1) & elective EFRT, pelvic node positive (IIIC1) & PRT, and PA node positive (IIIC2) & EFRT. Recurrence rates were lowest for patients with IIIC1 EFRT (5-year RFS 78.9%), but did not significantly differ from IIIC1 PRT (72.5%) or IIIC2 EFRT (69.3%, p =0.44). The 5-year OS rates were similar by group: 91.7% for IIIC1 EFRT, 86.5% for IIIC1 PRT, and 84.9% for IIIC2 EFRT (p=0.65). Of 31 patients with recurrence, most had distant relapse outside the RT field (16, 52%). In-field recurrences were local (3, 13%), regional (13%) or both (1, 3%). Of 78 IIIC1 patients treated with PRT, 7 patients (9%) had PA failure. Most patients with PA relapse had LVI (86%), ≥50% MMI (71%), & grade 3 disease (57%). Adjuvant RT results in excellent survival outcomes for patients with FIGO IIIC endometrial cancer. For patients with positive pelvic nodes, further study is warranted to determine if those with LVI, deep MMI & grade 3 disease benefit from EFRT.Abstract TU_21_3531; Table 1Patient CharacteristicsIIIC1 EFRTIIIC1 PRTIIIC2 EFRTp-value∗Wilcoxon rank sum, Kruskal-WallisN=32 (22.4%)N = 78 (54.5%)N = 33 (23.1%)Median Age (Range)57.5 (33-84)60.5 (41-78)57 (44-74)0.20Grade1238 (25.0)18 (56.3)6 (18.8)23 (29.5)33 (42.3)22 (28.2)11 (33.3)12 (36.4)10 (30.3)0.58LVI25 (78.1)53 (69.7)23 (71.9)0.77MMI ≥50%23 (71.9)49 (62.8)28 (84.8)0.16Gross residual diseaseInvolved LN VaginalOther01 (3.1)01 (1.3)0012 (36.4)01 (3.0)<.0001Median LNs dissected (Range)11.5 (2-46)13 (1-55)12 (0-39)0.99Median LNs involved (Range)1 (1-5)1 (1-10)3 (0-19)0.59Median EBRT dose in Gy (Range)45 (45-50.4)45 (45-56)45 (21.6-54)0.1Systemic Chemotherapy29 (92)63 (81)33 (100)∗ Wilcoxon rank sum, Kruskal-Wallis Open table in a new tab