Abstract Background In older patients, esophageal squamous cell carcinoma (ESCC) is difficult to treat using standard therapies, including surgery and cisplatin-based chemoradiotherapy. Paclitaxel (PTX) has radiosensitizing activity. We conducted a phase I trial of PTX combined with radiotherapy to establish a standard therapy for locally advanced ESCC in older patients. Methods Enrollment was conducted at six centers in Japan from April 2016 to September 2019. The participants were aged ≥ 70 years, had locally advanced ESCC, and were intolerant to surgery or unwilling. A fixed 60-Gy radiation dose was administered in 30 fractions. PTX dosing levels started at 30 mg/m2 weekly for 6 weeks. Depending on the number of DLTs, the dose was set to be increased by 10 mg/m2 or switched to biweekly. A geriatric assessment was performed before treatment using the Geriatric-8 screening tool. The primary endpoint was dose-limiting toxicity (DLT). Results We enrolled 24 patients (6 per group); DLT was observed in one (grade 4 hypokalemia), one (grade 3 aspiration), two (grade 3 radiodermatitis, grade 3 esophageal hemorrhage), and two (grade 3 anorexia, grade 5 pneumonitis) patients in the weekly PTX 30, 40, 50, and 60 mg/m2 groups, respectively. All adverse events, except death in the 60 mg/m2 group, showed reversible improvement, and the safety profile was considered acceptable. The 2-year survival and complete response rates were 40.0% and 54.2%, respectively. There was a significant difference in survival between favorable and unfavorable Geriatric-8 scores. Conclusions The recommended PTX dose with concomitant radiation was determined to be 50 mg/m2 weekly. Phase II trials at this dose are underway.
