Influence of radiation field on safety and efficacy for stage II/III esophageal cancer treated with definitive chemoradiotherapy: An exploratory analysis of JCOG0909

104 Background: JCOG0909, a single-arm confirmatory trial of definitive chemoradiotherapy (dCRT) including salvage treatment, demonstrated promising efficacy and safety for cStage II/III (UICC-TNM 6th) esophageal cancer (EC) (Ito Y, ASCO 2018). Radiation (RT) fields included the elective regional lymph node during initial 41.4 Gy, such as bilateral supraclavicular fossae and superior mediastinal lymph nodes for upper thoracic (Ut), and mediastinal and perigastric lymph nodes for middle thoracic (Mt)/lower thoracic (Lt) EC. It is unclear whether the safety and efficacy are associated with the tumor location in patients with cStage II/III EC treated with dCRT. Methods: Patients who were enrolled in JCOG0909 and underwent dCRT were analyzed. Patients were categorized into three groups according to primary tumor location (Ut/Mt/Lt). We compared adverse events during dCRT, complete response (CR) rate, progression-free survival (PFS) and overall survival (OS) among groups. Results: Ninety-four patients (Ut/Mt/Lt: 16/59/19) were analyzed. The proportions of cStage IIA/IIB/III were 31%/44%/25% in Ut group, 20%/42%/37% in Mt group, and 21%/32%/47% in Lt group, respectively. The summary of safety and efficacy was listed in Table 1. Grade 3-4 leukopenia, neutropenia and thrombocytopenia were more frequently observed in Mt and Lt groups than in Ut group. CR rate was 63% in Ut, 63% in Mt, and 42% in Lt, respectively. 3-year PFS in Ut/Mt/Lt was 60%/59%/47% and 3-year OS was 73%/78%/58%, respectively. Conclusions: The RT field by the tumor location might be associated with efficacy and safety of dCRT for cStage II/III esophageal cancer. [Table: see text]