Successful Salvage Therapy with Pomalidomide, Cyclophosphamide, and Dexamethasone for IgM Myeloma with t (11;14) and Dim CD38 Expression Refractory to Daratumumab, Lenalidomide, and Dexamethasone.

We herein present the case of a 73-year-old man with IgM multiple myeloma (IgM-MM) and t(11;14). The tumor cells showed a small lymphoplasmacytic morphology and dim expression of CD38 and CD138. The MYD 88L265P mutation was found to be negative. After plasma exchange, bortezomib and dexamethasone treatments were refractory. Subsequent daratumumab, lenalidomide, and dexamethasone therapy failed to respond despite the standard therapy for non-IgM-MM. Subsequently, pomalidomide, cyclophosphamide, and dexamethasone therapies demonstrated a good response, and a stringent complete response was therefore achieved. This case highlights the need for different treatment strategies for IgM-MM compared with non-IgM-MM because the biological features of IgM-MM and non-IgM-MM are different.