Background: In classical Hodgkin lymphoma (cHL), malignant Reed–Sternberg cells almost uniformly overexpress the programmed death receptor-1 (PD-1) ligands, PD-L1 and PD-L2, through genetic amplification at 9p24.1 [1]; therefore, cHL may be particularly sensitive to PD-1 blockade. Nivolumab (nivo), a fully human anti–PD-1 IgG4 monoclonal antibody checkpoint inhibitor, showed acceptable safety and high efficacy in a phase 1 trial (NCT01592370) of patients (pts) with relapsed/refractory cHL—a group with limited treatment options. Among 23 pts treated with nivo, investigator-assessed ORR was 87% and PFS at 24 weeks was 86% [2]. Median duration of response was not reached after 101 weeks [3]. Pts who progressed after stopping nivo were eligible for re-treatment. Aim: Assess the safety and efficacy of nivo re-treatment in pts with progression after initial response. Methods: In this phase 1 trial, adults with relapsed/refractory cHL were treated with nivo until progression, CR, or for a maximum of 2 years [3]. Pts with ongoing disease control (CR, PR, or stable disease) after discontinuation entered a protocol-specified follow-up period. Pts with PD <1 year after discontinuing nivo were eligible for re-treatment for ≤1 year. Toxicity, treatment response, and duration of response were assessed during re-treatment. Results: In total, 3 pts (age 26, 35, and 43 at baseline; 2 female) were re-treated with nivo. All had prior systemic treatment (4, 3, and 15, therapies, respectively) and had undergone autologous stem cell transplantation; 2 had prior treatment with brentuximab vedotin. ECOG performance status was 0 or 1. Nivo treatment course and outcomes are summarized in the Table. All 3 pts achieved a response with re-treatment. All experienced treatment-related AEs during the initial treatment period (1 grade 3 lymphopenia; all others grade 1–2). During re-treatment, 1 pt experienced treatment-related grade 2 neutropenia after 18 re-treatment cycles. Conclusion: All 3 pts re-treated with nivo responded to treatment, with 2 achieving PR and 1 discontinuing due to CR. These data provide preliminary evidence that re-treatment with nivo after progression may be an option for further treatment response. Funding: Bristol-Myers Squibb Previous presentation: Preliminary data on 1 patient presented at ASH 2015 References: