Secondary monoclonal gammopathy of unknown significance with isotype switching after CAR T-cell therapy for multiple myeloma: A case report

The incidence of secondary monoclonal gammopathy of undetermined significance is limited in patients with multiple myeloma post chimeric antigen receptor T-cell therapy. This is a case of secondary monoclonal gammopathy of undetermined significance with the appearance of distinct paraprotein peaks demonstrating isotype switching from IgA lambda to IgG lambda within 6 months post autologous chimeric antigen receptor T-cell therapy in a 66 year old multiple myeloma patient. Secondary monoclonal gammopathy of undetermined significance with or without isotype switching and/or new paraprotein bands may be a rare but important example of a benign and transient phenomenon representing pseudo-disease progression and potentially associated with longer progression-free survival and better overall outcomes. Although such association remains speculative given paucity of literature and an absence of high-quality data.