Patients with limited-stage SCLC (LS-SCLC) have a substantial unmet clinical need for new treatments that delay disease progression and prolong survival.In this phase 2, multicenter, randomized, multiarm, open-label trial, patients with untreated LS-SCLC received ociperlimab and tislelizumab plus concurrent chemoradiotherapy (cCRT) (arm A), tislelizumab plus cCRT (arm B), or cCRT (arm C). The primary objective was to compare progression-free survival (PFS) per investigator for arms A and B versus C (NCT04952597). The contribution of ociperlimab was explored by comparison of arms A versus B. Statistical analyses were descriptive, with no formal hypothesis testing.A total of 126 patients were randomized to arms A (N = 41), B (N = 42), and C (N = 43). The median PFS [95% confidence interval] exhibited a trend for improvement in arms A (12.6 [8.7-not estimable] months) and B (13.2 [8.5-not estimable]) compared with C (9.5 [8.3-14.4]); the PFS benefit was comparable between Arms A and B.The objective response rate, complete response rate, and median duration of response were numerically higher in arms A and B than in C. The median overall survival was not reached in all three arms, and the median distant metastasis-free survival revealed no trend for improvement for arms A and B compared with C. All patients experienced at least one treatment-related treatment-emergent adverse event.Ociperlimab and tislelizumab plus cCRT and tislelizumab plus cCRT exhibited a trend for improvement in PFS and numerically higher objective response rate compared with cCRT, with no new safety signals beyond the known profiles of immune checkpoint inhibitors and cCRT. Adding ociperlimab to tislelizumab plus cCRT was not associated with additional improvement in efficacy.© 2025 The Authors.