Rare plasma cell disorders—including IgD, IgE, and IgM multiple myeloma, non-secretory myeloma (NSMM), plasma cell leukemia (PCL), and heavy chain disease (HCD)—are biologically heterogeneous and often present with atypical features and aggressive behavior. This review synthesizes current evidence on their epidemiology, pathophysiology, diagnosis, and treatment. Advances in proteasome inhibitors, immunomodulatory agents, and autologous transplantation have improved outcomes in select subtypes. However, challenges persist in distinguishing IgM myeloma from Waldenström macroglobulinemia, monitoring non-secretory disease, and treating highly aggressive forms such as IgE myeloma and PCL. Standardized diagnostic criteria and prospective trials are essential to guide future management.

Haplo-HSCT with PTCy is now performed on a large scale worldwide. Our patient's outcomes did not completely reflect the results published by other groups. We herein present the results of 60 patients with hematologic malignancies treated homogeneously on a modified version of the standard protocol by adding ATG as an additional GvHD-prophylaxis measure. Retrospective analysis of 60 haplo-transplanted patients using myeloablative regimen with ATG and PTCy for GvHD prophylaxis. At 5-years the OS was 59.2%, the RFS was 48.6% and the CRFS was 40%. The median time to ANC and platelets engraftment was 16 and 28.5 days respectively. The grade II-IV aGvHD and extensive cGvHD were 46.7% and 23.3%. The cumulative incidence of relapse (CIR) was 30%, the NRM was 21.6% and the TRM was 11%. Higher DRI and 50% HLA-match were associated with lower RFS. Female to male donation and higher donor age were associated with higher cGvHD. The use of PTCy may not yield the same results in different populations. Many remaining questions need to be addressed in randomized trials (optimal graft source and donor, date of CNI initiation, personalized or targeted dose of PTCy, immune reconstitution, etc.).