Study on the Bone Marrow Plasma Cell Percentage in Predicting Survival in Newly Diagnosed Multiple Myeloma
Authors: Guan Tao , Zheng Meijing , Su Liping 
Published: December 2024

Introduction
In the diagnostic criteria for multiple myeloma (MM), the percentage of clonal plasma cells(PC) in bone marrow(BM)≥10% is one of the important diagnostic criteria. However, the count of PC is greatly affected by the detection method. The BM smear staining processing is simple and has low damage to cells, but it cannot detect the clonality of PC; BM biopsy(BMB) is complex and time-consuming, and the PC count is greatly affected by human factors; flow cytometry (FCM) can detect the clonality of PC, but it has high requirements for cell activity, and the test procedure is easy to cause cell damage, resulting in a PC percentage lower than the true value. In clinical practice, there is a confusion of inconsistency between the PC percentage detected by BM smear and FCM, and there are few reports on the PC percentage detected by the two methods in predicting MM survival. This study enrolled patients with newly diagnosed MM (NDMM) for retrospective analysis to explore the clinical value of the PC percentage detected by the two methods.
Methods
147 NDMM from Shanxi province cancer hospital from January 2018 to December 2023 were enrolled in this study. The diagnosis of patients met the 2014 IMWG diagnostic criteria. After Wright-Giemsa staining of BM smear, the PC percentage is calculated by the ratio of PC to nuclear cells. Clonal PC detected by FCM, and abnormal immunophenotype included CD19(-) /CD45 (-/dim) /CD56(+) /CD117(+) /CD27(-)/CD81(-), and restricted expression of Kappa/Lambda. Clonal PC percentage is calculated by the ratio of clonal PC to nuclear cells. The induction treatment regimen is the combination of proteasome inhibitors, immunomodulatory drugs, cytotoxic drugs and autologous hematopoietic stem cell transplantation (auto-HSCT). All patients were followed up regularly, and the median follow-up time is 25.13 months (0.46-66.67 months).
Results
We analyzed the correlation between bone marrow PC percentage and poor clinical prognostic factors and showed that PC percentage was significantly higher in patients with advanced R-ISS stage, higher risk stratification(mSMART stratification), elevated lactate dehydrogenase (LDH), and higher β2 microglobulin(β2M). These differences were consistent in BM smear PC percentage and FCM PC percentage. NDMM patients with BM smear PC percentage &gt;50% had a significantly shorter OS and PFS than those with BM smear PC percentage ≤50% (p=0.0034, p=0.0538 ); When the FCM PC percentage &gt;10%, the OS and PFS of NDMM patients are significantly worse than those with the FCM PC percentage ≤10% (p=0.0073, p=0.0348). We also explored the effect of auto-HSCT on OS and PFS. The results showed that patients who underwent auto-HSCT had better OS and PFS than those who did not undergo auto-HSCT; Patients with higher PC percentage who underwent ASCT still had better OS and PFS than patients with lower PC percentage but who did not undergo transplantation.
Conclusions
Our data demonstrated that the bone marrow PC percentage can reflect tumor burden and is associated with patient survival. Higher PC percentage predict the Shorter OS and PFS of NDMM. ASCT induction therapy can improve the poor survival outcome caused by increased PC percentage.