Background: JCOG0909 is a phase II trial of definitive chemoradiotherapy including salvage treatment for cStage II–III thoracic esophageal cancer; the radiation field for elective regional lymph node irradiation, which can affect patient outcome and adverse event, varied based on the primary tumor site, i.e., upper (Ut), middle (Mt), and lower thoracic (Lt) esophagus. The impact of different primary sites on the safety and efficacy of definitive chemoradiotherapy in JCOG0909 is not well characterized. Methods: Patients were categorized into three groups (Ut, Mt, and Lt) according to the primary tumor location. We compared acute adverse events during definitive chemoradiotherapy, complete response (CR) rate, 3-year progression-free survival (PFS), and overall survival (OS) among the 3 groups. Results: Out of the 96 patients enrolled in JCOG0909 between April 2010 and August 2014, 94 patients (16, 59, and 19 patients in the Ut, Mt, and Lt groups, respectively) were included in this exploratory analysis. The proportion of patients with cStage III was 25% in the Ut, 37% in the Mt, and 47% in the Lt group. Grade 3–4 leukopenia, neutropenia, and thrombocytopenia were more frequently observed in the Mt (66%, 54%, and 15%) and Lt groups (84%, 68%, and 16%) than in the Ut group (38%, 44%, and 0%). There was no significant between-group difference with respect to 3-year OS (73.3%, 77.9%, and 57.9%), 3-year PFS (60.0%, 59.3%, and 47.4%), or CR rate (62.5%, 62.7%, and 42.1%). Conclusions: In JCOG0909, the incidence of severe hematological toxicity had a trend toward higher in the Mt and Lt than the Ut esophageal cancer; however, no remarkable difference by primary sites was observed with respect to efficacy endpoints.
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