Phase 2 Study of Stereotactic Body Radiation Therapy for Patients with Oligometastatic Esophageal Squamous Cell Carcinoma

This study aims to assess the safety and efficacy of stereotactic body radiation therapy (SBRT) for patients with oligometastatic esophageal squamous cell carcinoma (ESCC).From April 2015 to December 2018, a prospective, single-arm, phase 2 trial was conducted. The main inclusion criteria were ESCC patients with 3 or fewer metastases and a controlled primary malignancy after radical treatment, with all metastatic lesions amenable to SBRT. The enrolled patients were assigned to SBRT for all metastatic lesions and then received chemotherapy for at least 4 cycles starting from 0 to 15 days after SBRT. The primary endpoint was progression-free survival (PFS). Overall survival, local control, and toxicities were assessed in all patients. The study is listed at clinicaltrials.gov, number NCT03000816.Thirty-four patients with 40 oligometastatic lesions, including 25 in distant organs and 15 in nonregional lymph nodes, were treated with SBRT. All metastases belonged to genuine oligometastatic disease. Seventeen patients (50.0%) received a median of 4 cycles (interquartile range, 3-6 cycles) of chemotherapy after SBRT. At a median follow-up time of 18.2 months (interquartile range, 11.1-35.0 months), the median PFS time was 13.3 months (95% confidence interval, 10.7-15.9); the 1- and 2-year PFS rates were 55.9% and 33.8%, respectively. The 1- and 2-year overall survival rates were 76.2% and 58.0%, respectively. The 1- and 2-year local control rates were both 92.1%. Grade 3 acute toxicities were observed in only 1 patient. No grade ≥4 acute adverse events or grade ≥3 late adverse events due to SBRT occurred in this study.For well-selected patients with oligometastatic ESCC, SBRT with or without chemotherapy is a well-tolerated and efficacious treatment modality. The prognosis of oligometastatic ESCC is quite different from that of extensively metastatic ESCC, so treatment with an accurate stratification for patients with metastatic ESCC is necessary.