Soluble B-cell Maturation Antigen in Multiple Myeloma and Correlation With Response to Therapy

B-cell maturation antigen (BCMA) is a nontyrosine kinase receptor expressed during plasma cell differentiation. Binding of ligands such as APRIL and BAFF to BCMA on malignant plasma cells leads to proliferation of tumor cells and plays an important role in the pathogenesis of multiple myeloma. Recent studies have explored the role of serum-soluble BCMA (sBCMA) in assessing tumor load as well as monitoring of response. In this study, we aimed to detect serum sBCMA levels in newly diagnosed multiple myeloma patients as well as monitor the levels at follow-up to correlate with response to therapy.

This was a prospective, longitudinal study conducted between March 2023 and July 2024. We documented the routine disease characteristics along with sBCMA levels at baseline and followed up sBCMA levels as a marker of therapy response.

Baseline sBCMA levels were significantly higher in patients presenting with anemia and hypercalcemia and in patients having high-risk cytogenetics. There was a trend toward correlation of sBCMA levels with bone marrow plasma cell percentage, β2-microglobulin, and thrombocytopenia. We also found significant association of the sBCMA level with both ISS and R-ISS staging. Furthermore, we assessed the response to therapy in terms of IMWG response criteria and sBCMA-based response. The response according to conventional response criteria correlated significantly with sBCMA-based response. We also found a significant association of decline in sBCMA levels to that of M band on response to therapy. There are certain advantages of using sBCMA as a response monitoring tool, such as in patients with renal impairment and in nonsecretory myeloma.

Our study provides an important insight into the relation of sBCMA to disease characteristics and the kinetics of decline in sBCMA on response to therapy.