Short-course neoadjuvant radiotherapy combined with chemotherapy and toripalimab for locally advanced esophageal squamous cell carcinoma (SCALE-1): a single-arm phase Ib clinical trial

Background: The optimal dosages, timing, and treatment sequencing for standard-of-care neoadjuvant chemoradiotherapy necessitate re-evaluation when used in conjunction with immune checkpoint inhibitors for patients with resectable, locally advanced esophageal squamous cell carcinoma (RLaESCC). The SCALE-1 phase Ib study aimed to evaluate the safety and efficacy of short-course neoadjuvant radiotherapy combined with chemotherapy and toripalimab in this patient population.

Methods: RLaESCC patients with clinical stages cT3-4aN0M0/cT1-4aN+M0 received neoadjuvant paclitaxel (135 mg/m²), carboplatin (area under the curve=5), and toripalimab (240 mg) every 3 weeks for two cycles. Short-course neoadjuvant radiotherapy (30 Gy in 12 fractions; 5 days per week) was administered between neoadjuvant immune-chemotherapy (nICT) doses. Esophagectomies were scheduled 4-6 weeks after completing neoadjuvant treatment. The primary endpoint was safety, with secondary endpoints including pathological complete response (pCR) rate, postoperative complications, progression-free survival (PFS), and overall survival (OS). Exploratory biomarker analysis used gene expression profiles via the nCounter platform.

Results: Of the 23 patients enrolled, all completed neoadjuvant radiotherapy, while 21 cases finished full nICT doses and cycles. Common grade 3/4 adverse events included neutropenia (57%), leukopenia (39%), and skin rash (30%). No grade 3 or higher esophagitis or pneumonitis occured. Twenty patients underwent surgery, and 11 achieved pCR (55%). Two patients (10%) experienced grade IIIb surgical complications. At the database lock, a 2-year PFS rate of 63.8% (95% CI 43.4% to 84.2%) and 2-year OS rate was 78% (95% CI 64.9% to 91.1%) were achieved. Tumor immune microenvironment analysis indicated that tumors with pCR exhibited significantly higher pretreatment T-cell-inflamed score and post-treatment reshaping of antitumor immunity.

Conclusions: Combining short-course neoadjuvant radiotherapy with chemotherapy and toripalimab demonstrated favorable safety and promising efficacy in RLaESCC patients.

Trial registration number: ChiCTR2100045104.