CD19 CAR T‐Cell Therapy for Primary Mediastinal Large B‐Cell Lymphoma: A CIBMTR Analysis

T cells engineered with CD19-directed chimeric antigen receptors (CD19 CAR) T cells have become standard treatment for patients with high risk, relapsed or refractory (R/R) large B-cell lymphomas (LBCL). However, outcomes in patients with rare subsets of LBCL, such as primary mediastinal large B-cell lymphoma (PBMCL), have not been well characterized. The impact of prior immune checkpoint inhibitor (ICI) treatment, commonly used to treat R/R PMBCL, is also unknown. To address these gaps, we retrospectively analyzed CIBMTR registry data including PMBCL patients undergoing CD19 CAR T-cell therapy per standard-of-care. A total of 135 PMBCL adults from 66 centers were included. Median age at the time of CAR T-cell therapy was 32. Thirty-nine patients (28.9%) had received an ICI prior to CAR T-cell therapy. The best overall and complete response (CR) rates after CD19 CAR T-cell therapy were 79% and 67.7%, respectively. The 2-year progression-free (PFS) and overall survival (OS) were 58.6% (95% CI, 49.7-67.3) and 80.8% (95% CI, 72.6-87.8), respectively. The 2-year cumulative incidence (CI) of relapse and non-relapse mortality (NRM) were 36% (95% CI, 27.8-44.7) and 5.4% (95% CI, 1.9-10.5), respectively. We observed grade ≥ 3 CRS and ICANS in 6.1% and 14.7%, respectively. Prior ICI exposure was associated with lower 2-year CI of relapse (ICI-exposed, 21.7%; ICI-naïve, 41.6%; p = 0.03) and higher 2-year NRM (ICI-exposed, 11.7%; ICI-naïve, 2.8%; p = 0.03). We could not confirm statistically different PFS (p = 0.19) or OS (p = 0.26) between ICI-exposed and ICI-naïve patients. CD19 CAR T-cell therapy led to high rates of durable responses in PMBCL patients with low rates of severe toxicities.