571. A PHASE I/II MULTICENTER STUDY EVALUATING THE EFFICACY AND SAFETY OF INDUCTION IMMUNOCHEMOTHERAPY FOLLOWED BY CONCURRENT IMMUNO-CHEMORADIOTHERAPY IN UNRESECTABLE LA-ESCC

Abstract Background Despite advances in radiotherapy techniques, the prognosis for patients undergoing definite chemoradiotherapy remains suboptimal. There exists an urgent and unmet need to enhance the efficacy of concurrent chemoradiotherapy for patients with unresectable Locally Advanced Esophageal Squamous Cell Carcinoma (LA-ESCC). Immunotherapy, when combined with chemotherapy, has emerged as the established first-line treatment for advanced esophageal cancer. Significant tumor shrinkage and reduced tumor residual observed after induction immunotherapy might provide the potential to enhance locoregional control of radiotherapy as well as better protection of critical organs and circulating lymphocytes. Methods We conducted a multicenter, phase I/II study aiming to assess the efficacy and safety of induction immunochemotherapy followed by immuno-chemoradiotherapy (ICRT) for unresectable LA-ESCC (SCR-ESCC-002, NCT06173986) (Figure 1). Eligible patients will initiate treatment with 2-3 cycles of immunochemotherapy. Within 4 weeks after completing the induction treatment, patients without disease progression will proceed to receive concurrent radiotherapy (45-50Gy in 25 fractions), weekly chemotherapy, and PD-1 inhibitor on day1,22. Following immuno-chemoradiotherapy, patients will continue with immunotherapy maintenance until disease progression or unacceptable toxicity, for a maximum duration of one year. The study's dual primary endpoints are progression-free survival and treatment completion rate. Results As of January 2024, 13 eligible patients were enrolled in our trial, with median follow-up of 7.8 months. Due to tumor shrinkage of induction immunochemotherapy, radiation doses to normal tissues were significantly reduced, particularly for the lungs, heart, and vertebrae. All 13 patients completed the planned induction treatment and radiotherapy, with 8 completing more than 4 weekly chemotherapies. During ICRT, 10 of 13 patients experienced grade 3-4 adverse events. These included lymphopenia (69.23%), myelosuppression (46.15%), hepatitis (7.69%), esophagitis (7.69%), and pneumonitis (7.69%). Nine patients achieved a complete response, and 3 partial response 4 weeks after ICRT according to RECIST v1.1. Conclusion Decreased radiation volumes due to tumor regression brought by induction immunochemotherapy diminish the occurrence of non-hematological adverse events during ICRT. Preliminary analysis suggests that this therapeutic modality exhibits favorable safety profiles and yields a superior clinical complete response rate compared to definitive chemoradiotherapy alone. The trial is presently enrolling participants, and the confirmation of efficacy and survival outcomes necessitates larger sample sizes and extended follow-up durations.