Background: Tislelizumab is a humanized IgG4 monoclonal antibody with high affinity/specificity for programmed cell death protein 1 (PD-1). It was engineered to minimize binding to Fc-γ receptors on macrophages, thereby decreasing antibody-dependent phagocytosis, a potential mechanism of T-cell clearance and resistance to anti–PD-1 therapy. Tislelizumab therapy was highly active in autologous stem cell transplant (ASCT)-failed or ineligible patients with R/R cHL (Leukemia. 2020;34:533). Here we report results from up to 3 years follow-up. Methods: This asingle-arm, multicenter phase 2 study (NCT03209973) of 200 mg tislelizumab administered intravenously to patients (pts) with R/R cHL every 3 weeks until progressive disease (PD) or unacceptable toxicity. Patients were eligible if they: failed to achieve a response or progressed after ASCT, or: received ≥2 lines of prior systemic chemotherapy for cHL and were ineligible for ASCT. Primary endpoint was overall response rate (ORR) assessed by an independent review committee (IRC) per Lugano criteria (J Clin Oncol. 2014;32:3059). Secondary endpoints were progression-free survival (PFS), duration of response (DOR), complete response (CR) rate, and time to response (TTR) per IRC, safety, and tolerability. Results: Pts (N=70) from 11 centers in China were enrolled and treated; characteristics have been previously reported. As of the data cutoff date (Nov 2, 2020), median follow-up was 33.8 months (range, 3.4-38.6). Pts still on treatment at the end of study (n=33; 47.1%) entered a long-term extension study. Efficacy data is presented in the Table below. In the 13 pts who received prior ASCT, 11 (84.6%) achieved CR. The most common treatment-emergent adverse events (AEs; ≥30%) were pyrexia (57.1%), upper respiratory tract infection (38.6%), hypothyroidism (37.1%), and increased weight (34.3%). Treatment-related grade ≥3 AEs (≥2 pts) were pneumonitis, hypertension, neutropenia, lipase increased, weight increased, and increased creatine phosphokinase (CPK; 2.9% each). Immune-related AEs were reported in 32 pts (45.7%), with grade ≥3 AEs in 8 pts (11.4%): pneumonitis (4) and skin adverse reactions, nephritis, lipase increased, and blood CPK increased (1 each). AEs led to treatment discontinuation in 6 pts (8.6%). Conclusions: Long-term follow-up of R/R cHL pts treated with tislelizumab further demonstrated the substantial therapeutic activity and continued PFS benefit. There were no new safety concerns identified for long-term treatment with tislelizumab. Clinical trial information: NCT03209973

m, median; NE, not estimable; OS, overall survival. *Two-sided Clopper-Pearson 95% CI. ^†Based on Kaplan-Meier estimation.