Clinical Characteristics and Prognosis of Primary Plasma Cell Leukemia and Newly Diagnosed Multiple Myeloma Under the New IMWG Definition Criteria

Background: Recently, the International Myeloma Working Group (IMWG) has recommended new primary plasma cell leukemia (pPCL) definition criteria, which require the presence of ≥ 5% circulating plasma cells in peripheral blood smears. The objective of this study was to investigate the clinical characteristics and prognosis of new-defined pPCL and newly diagnosed multiple myeloma (NDMM).

Methods: This was a single-center, retrospective study including patients diagnosed with new-defined pPCL or NDMM at Zhongda Hospital, China, between January 2010 and December 2022.

Results: There were 23 pPCL patients and 264 NDMM patients in our cohort. Generally, pPCL patients were younger than NDMM patients (median diagnostic age: 63 vs. 67 years old, p=0.018). The 1q21+ aberration was predominantly found in NDMM (p= 0.038) whereas t(11;14) dominated in pPCL (p= 0.017). Notably, pPCL exhibited a lower platelet level (p< 0.001) and a higher frequency of non-hyperdiploid karyotypes (p= 0.03) in contrast to NDMM. The median overall survival (OS) and progression-free survival (PFS) in NDMM were notably superior to those observed in pPCL (HR: 0.41, p= 0.001, HR: 0.38, p< 0.001, respectively). Interestingly, the OS in NDMM was 3 times longer than that in pPCL in females (p< 0.01) while no difference was found between NDMM and pPCL in males (p= 0.078). Moreover, NDMM patients treated with proteasome inhibitor (PI)-based treatment showed a significantly better prognosis than pPCL patients receiving the same treatment (OS: p< 0.01, PFS: p< 0.01, respectively). Similar findings were observed for patients undergoing either autologous stem cell transplantation (ASCT) or CD38 antibody treatment, both presenting a favorable prognosis in NDMM. However, no significant difference emerged between the two groups in terms of immunomodulatory drugs (IMiDs)-based or PI+IMiDs-based regimens. Multivariate analysis indicated elevated lactate dehydrogenase (LDH) was an independent predictor of adverse prognosis in NDMM (HR: 3.12, p<0.01).

Conclusion: Our study revealed the clinical features and prognosis of pPCL and NDMM patients according to the new diagnostic criteria. The findings highlighted a generally improved prognosis in NDMM compared to pPCL, especially among female patients or those treated with PI-based regimens. It is important to note that our study had a limited sample size, potentially introducing some bias. We hope well-designed and long-term follow-up studies can be conducted to provide more reliable results.