Consolidative radiotherapy for residual FDG activity on day +30 post CAR T-cell therapy in non-Hodgkin lymphoma

Abstract

Majority of non-Hodgkin lymphoma (NHL) patients who achieve partial response (PR) or stable disease (SD) to CAR T-cell therapy (CART) on day+30 progress and only 30% achieve spontaneous complete response (CR). This study is the first to evaluate the role of consolidative radiotherapy (cRT) for residual FDG activity on day+30 post-CART in NHL. We retrospectively reviewed sixty-one patients with NHL who received CART and achieved PR or SD on day+30. Progression-free survival (PFS), overall survival (OS), and local relapse-free survival (LRFS) were assessed from CART infusion. cRT was defined as comprehensive – treated all FDG-avid sites – or focal. Following day+30 PET scan, 45 patients were observed and 16 received cRT. Fifteen (33%) observed patients achieved spontaneous CR, and 27 (60%) progressed with all relapses involving initial sites of residual FDG activity. Ten (63%) cRT patients achieved CR, and 4 (25%) progressed with no relapses in the irradiated sites. The 2-year LRFS was 100% in the cRT sites and 31% in the observed sites (p<0.001). The 2-year PFS was 73% and 37% (p=0.025) and the 2-year OS was 78% and 43% (p=0.12) in the cRT and observation groups, respectively. Patients receiving comprehensive cRT (n=13) had superior 2-year PFS (83% vs 37%, p=0.008) and 2-year OS (86% vs 43%, p=0.047) compared to observed or focal cRT patients (n=48). NHL patients with residual FDG activity following CART are at high risk of local progression. cRT for residual FDG activity on day+30 post-CART appears to alter the pattern of relapse and improve LRFS and PFS.