e19507 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. [Table: see text]
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