[The expression level of secretory mature B cell surface antigen in primary diagnosed multiple myeloma and its clinical significance].

Objective: To explorer Secretory mature B cell surface antigen (sBCMA) expression level, changes during treatment and clinical significance in newly diagnosed MM patients. Methods: Clinical data of 158 MM patients admitted to the Department of Hematology, the First Affiliated Hospital of Soochow University from August 2018 to September 2020 were analyzed retrospectively. The concentration of sBCMA in the patients was determined by BCMA ELISA and compared with the normal range. The results were compared with clinical efficacy, age, type, R-ISS stage, renal impairment, and humoral immune function. Results: The median age of the patients was 57 (31-73 years old), 86 (54.5%) males and 72 (45.5%) females, mainly IgG type, 81 patients(51.2%). SBCMA value M ( Q 1 , Q 3 ) was 76.50 (55.50, 94.40) μg/L, 100% higher than the upper limit of normal value. According to the efficacy evaluation, the patients were divided into complete remission(CR) group, very good partial remission(VGPR) group, partial remission(PR) group and ineffiecacy group, the results showed the level of sBCMA in CR group[80.10 (58.05, 96.90) vs 15.70 (9.85, 28.65) μg/L] and VGPR group[74.60 (52.20, 93.00) vs 17.20 (13.30, 38.80) μg/L]was significantly higher than that before treatment(all P <0.001), and there was no significant difference in PR group and ineffective group before and after treatment (all P >0.05).The amount of serum intact protein M protein was positively correlated with the level of sBCMA expression in newly diagnosed patients ( r= 0.22, P =0.040), and there was no correlation between the proportion of bone marrow plasma cells and sBCMA expression ( r =0.07, P =0.449).The correlation between sBCMA levels at initial diagnosis and MM type[IgG type, IgA type vs light chain type:(78.6±3.5), (72.4±5.4) vs (83.8±6.9)μg/L], age[≥65 vs<65 years: (73.6±5.5)vs (79.3±3.1)μg/L], R-ISS stage[stage Ⅰ, Ⅱ vs Ⅲ:(80.2±3.1) vs (69.4±6.1)μg/L], renal impairment [Creatinine clearance rate (Ccr) ≤30 vs>30 ml/min:(81.6±4.8) vs (76.5±3.4)μg/L], and high-risk karyotype[high-risk vs standard-risk:(73.6±5.7) vs (80.2±3.2)μg/L] were not associated (all P >0.05). Expression levels of sBCMA were negatively correlated with IgM levels in MM patients ( r =-0.39, P =0.002) and after treatment ( r =-0.25, P =0.015). Conclusions: The expression of sBCMA in MM patients is a reliable indicator of the clinical efficacy of MM and is related to the occurrence of MM immune deficiency and recovery after treatment. sBCMA can be used as a new independent marker for monitoring and predicting the efficacy of MM patients.