Outcomes and treatment patterns in primary and secondary plasma cell leukemia: insights from a large US cohort study

Plasma cell leukemia (PCL) is a rare and aggressive plasma cell disorder with a short survival duration despite the use of novel therapeutics. PCL remains an understudied disease for which there is no current standard of care treatment. Knowledge on optimal novel drug sequencing, including the role and timing of hematopoietic stem cell transplant as primary and salvage therapy is needed. We conducted a large retrospective analysis of 153 PCL patients, using the new definition of ≥5% circulating plasma cells, including clinical features and treatment outcomes across seven academic centers in the United States. This is, to the best of our knowledge, the largest multicenter study conducted in the US of this rare disease. Disease presentation, clinical and genetic characteristics, and treatment patterns of 93 patients with primary PCL and 57 with secondary PCL are described. Additionally, associations between patient characteristics and mortality were investigated using Cox proportional hazards regression models. Secondary PCL was associated with a worse prognosis, with a median overall survival of 3.2 months compared to 36.6 months for primary PCL (P<0.001). Receipt of a transplant was associated with a survival advantage in both primary PCL (Hazard Ratio [HR] 0.16, P<0.001) and secondary PCL (HR 0.20, P=0.001). No significant difference in outcomes was observed between proteasome inhibitor-based triplet regimens and the VTD-PACE like regimen. The presence of extramedullary disease and high-risk cytogenetics was not associated with survival in the primary PCL group.