Patterns of relapse in patients with multiple myeloma receiving chimeric antigen receptor T cell therapy: a multi-center analysis

To the Editor:

Extramedullary disease (EMD) is a risk factor for poor outcomes in multiple myeloma (MM) [1,2,3], including amongst recipients of chimeric antigen receptor T-cell therapy (CAR-T) [4, 5]. With CD-19 CAR-T, discordant responses have also been observed, with clearance of disease in the marrow and persistence of disease in extramedullary sites, highlighting how CAR-T activity may be limited in extramedullary sites [6]. While patterns of progression at relapse have been studied, no prior work has specifically examined relapse patterns in CAR-T recipients with MM [7, 8]. Most early disease progressions are biochemical, highlighting the importance of routine bloodwork [7, 8]. The percentage of biochemical relapses that precede a clinical relapse in the post-CAR-T setting remains to be determined, as does the frequency of relapses with EMD or end-organ damage despite extensive surveillance.