The clinical characteristics of patients with primary plasma cell leukemia and the efficacy of novel agents and hematopoietic stem cell transplantation

Objective: To analyze the immunophenotype and cytogenetic characteristics of primary plasma cell leukemia (pPCL), and to evaluate the efficacy of bortezomib and hematopoietic stem cell transplantation as main treatment. Methods: A retrospective cohort study was conducted including 42 pPCL patients admitted to Peking University People's Hospital from January 1998 to March 2019. All patients were followed up until December 31, 2019. The immunophenotype and cytogenetic characteristics were compared with historical data of multiple myeloma (MM). Thirty-nine patients were divided into bortezomib-based group (29 cases) and non-bortezomib group (10 cases). All patients were also divided into hematopoietic stem cell transplantation (HSCT) group (15 cases) and non-HSCT group (24 cases).Chi-square test was used for efficacy comparison, and Kaplan-Meier method was used for univariate prognostic analysis. Cox proportional hazards model was used for multi-variant analysis. Results: pPCL accounted for 2.6% of the total patients with plasma cell diseases during the same period. There were 22 males and 20 females, with a median age of 50 (30-77) years old at diagnosis. In immunophenotype analysis, tumor cells in pPCL patients also expressed CD38, CD138, CD45, which was similar as patients with MM. However the expression of CXCR4 were more frequently seen in pPCL(73.1% vs. 34.7%, P= 0.000), while intensity of CD9 and CD200 was lower (40.7% vs. 62.5%, P =0.028, 33.3% vs. 58.0%, P=0.021).Overall response rate of bortezomib-based therapy was superior to non-bortezomib therapy (69.0% vs.50.0%). The median survival was 18.2 (0.2-95.7)months, and the 1-and 2-year survival rates were 61.9% and 37.4%, respectively. Multivariate prognostic analysis suggested that age (P= 0.027) and efficacy(P= 0.035)were significantly correlated with survival.HSCT resulted in superior survival compared with chemotherapy alone(26.8 vs. 8.1 months, P=0.021). Conclusions: Immunophenotypes and cytogenetic abnormalities in patients with pPCL are different from those with multiple myeloma. Bortezomib based regimens improve response rate and survival of pPCL. Hematopoietic stem cell transplantation also predicts survival benefits.