PO49

Purpose To investigate practice patterns in adjuvant radiation (RT) delivery for patients with FIGO stage II endometrioid endometrial adenocarcinoma treated between 2004-2019. Materials and Methods The National Cancer Database (NCDB) was queried to review patients diagnosed between 2004-2019 with FIGO stage II endometrioid endometrial adenocarcinoma who underwent total hysterectomy and bilateral salpingo-oophorectomy (TH/BSO) and surgical staging. Multivariate regression analysis (MVA) was used to identify prognostic variables for adjuvant RT and RT omission. Results A total of 18,798 patients met inclusion criteria. Median follow-up was 6 years. Median age was 60 years. Twelve percent of patients received chemotherapy (CHT), and 68% received adjuvant RT. Of the study population, 19% received external beam radiation (EBRT) alone, 25% received vaginal brachytherapy (VBT) alone, and 24% received EBRT+VBT. Of those who received CHT, 35% received CHT alone whereas 25% also received EBRT alone, 22% received VBT alone, and 18% received EBRT+VBT. Use of adjuvant RT, including EBRT, VBT, and EBRT+VBT, increased over time, and EBRT+VBT was the most common treatment in 2019 (34% vs 23% in 2004; see Figure 1). On MVA, treatment at a community hospital (OR 1.8, p<0.001) or in the Midwest (OR 1.2, p=0.02), receipt of single agent chemotherapy (OR 6.9, p<0.001), LVSI+ (OR 1.4, p<0.001), and positive surgical margins (OR 1.8, p<0.001) were associated with increased likelihood of receiving any EBRT. No factors were significantly associated with an increased likelihood of receiving any VBT. Age >60 years old (OR 0.86, p=0.02), treatment at a community hospital (OR 0.41, p<0.001), distance from a treatment center >50 miles (OR 0.72, p<0.001), and grade 2 (OR 0.86, p=0.02) or 3 (OR 0.80, p=0.01) disease were associated with decreased likelihood of receiving VBT. Regionally, patients treated in the Midwest (OR 0.84, p=0.02), South (OR 0.54, p<0.001), or West (OR 0.52, p<0.001) were less likely to have received VBT compared to those in the Northeast. Black race (OR 1.2, p=0.03), treatment at a community hospital (OR 1.4, p=0.04), treatment in the South (OR 2.2, p<0.001) or West (OR 2.1, p<0.001), distance from a treatment center >50 miles (OR 1.5, p<0.001), and grade 2 (OR 1.2, p<0.001) or 3 (OR 1.3, p=0.01) disease were associated with an increased likelihood of RT omission. In contrast, receipt of single agent chemotherapy (OR 0.14, p<0.01), >50% myometrial invasion (OR 0.58, p<0.001), and positive surgical margins (OR 0.66, p=0.03) were associated with a decreased likelihood of RT omission. Conclusions Treatment guidelines for FIGO stage II endometrioid endometrial carcinoma support a variety of adjuvant treatment options with little data to direct selection of adjuvant therapy after surgery. Use of adjuvant RT has increased over the years, particularly the use of both EBRT+VBT. Patient-related factors such as race, region, and distance from treatment center were associated with RT omission whereas tumor-related risk factors such as positive surgical margins, LVSI, and myometrial invasion were associated with use of EBRT. Adjuvant RT use varied geographically, particularly in the use of VBT. Optimal choice of adjuvant therapy remains uncertain; however, identifying these patterns can help guide research to more definitively direct adjuvant treatment guidelines and may help identify gaps or biases in adjuvant RT practices. To investigate practice patterns in adjuvant radiation (RT) delivery for patients with FIGO stage II endometrioid endometrial adenocarcinoma treated between 2004-2019. The National Cancer Database (NCDB) was queried to review patients diagnosed between 2004-2019 with FIGO stage II endometrioid endometrial adenocarcinoma who underwent total hysterectomy and bilateral salpingo-oophorectomy (TH/BSO) and surgical staging. Multivariate regression analysis (MVA) was used to identify prognostic variables for adjuvant RT and RT omission. A total of 18,798 patients met inclusion criteria. Median follow-up was 6 years. Median age was 60 years. Twelve percent of patients received chemotherapy (CHT), and 68% received adjuvant RT. Of the study population, 19% received external beam radiation (EBRT) alone, 25% received vaginal brachytherapy (VBT) alone, and 24% received EBRT+VBT. Of those who received CHT, 35% received CHT alone whereas 25% also received EBRT alone, 22% received VBT alone, and 18% received EBRT+VBT. Use of adjuvant RT, including EBRT, VBT, and EBRT+VBT, increased over time, and EBRT+VBT was the most common treatment in 2019 (34% vs 23% in 2004; see Figure 1). On MVA, treatment at a community hospital (OR 1.8, p<0.001) or in the Midwest (OR 1.2, p=0.02), receipt of single agent chemotherapy (OR 6.9, p<0.001), LVSI+ (OR 1.4, p<0.001), and positive surgical margins (OR 1.8, p<0.001) were associated with increased likelihood of receiving any EBRT. No factors were significantly associated with an increased likelihood of receiving any VBT. Age >60 years old (OR 0.86, p=0.02), treatment at a community hospital (OR 0.41, p<0.001), distance from a treatment center >50 miles (OR 0.72, p<0.001), and grade 2 (OR 0.86, p=0.02) or 3 (OR 0.80, p=0.01) disease were associated with decreased likelihood of receiving VBT. Regionally, patients treated in the Midwest (OR 0.84, p=0.02), South (OR 0.54, p<0.001), or West (OR 0.52, p<0.001) were less likely to have received VBT compared to those in the Northeast. Black race (OR 1.2, p=0.03), treatment at a community hospital (OR 1.4, p=0.04), treatment in the South (OR 2.2, p<0.001) or West (OR 2.1, p<0.001), distance from a treatment center >50 miles (OR 1.5, p<0.001), and grade 2 (OR 1.2, p<0.001) or 3 (OR 1.3, p=0.01) disease were associated with an increased likelihood of RT omission. In contrast, receipt of single agent chemotherapy (OR 0.14, p<0.01), >50% myometrial invasion (OR 0.58, p<0.001), and positive surgical margins (OR 0.66, p=0.03) were associated with a decreased likelihood of RT omission. Treatment guidelines for FIGO stage II endometrioid endometrial carcinoma support a variety of adjuvant treatment options with little data to direct selection of adjuvant therapy after surgery. Use of adjuvant RT has increased over the years, particularly the use of both EBRT+VBT. Patient-related factors such as race, region, and distance from treatment center were associated with RT omission whereas tumor-related risk factors such as positive surgical margins, LVSI, and myometrial invasion were associated with use of EBRT. Adjuvant RT use varied geographically, particularly in the use of VBT. Optimal choice of adjuvant therapy remains uncertain; however, identifying these patterns can help guide research to more definitively direct adjuvant treatment guidelines and may help identify gaps or biases in adjuvant RT practices.