Investigation of IgM Monoclonal Paraprotein in Bone Marrow Aspiration: the Role of Immunophenotyping by Flow Cytometry in Selecting Cases for Molecular Testing for the P.myd88 L265P Point Mutation.

BACKGROUND:Flow cytometry and real-time quantitative polymerase chain reaction (qRT-PCR) for MYD88 mutations (MYD88mt) are routinely performed on bone marrow aspirates during the diagnostic evaluation of IgM monoclonal paraproteinemia. The potential predictive value of immunophenotypic findings for molecular results, however, remains to be fully clarified. OBJECTIVE:This study aimed to determine whether the presence or absence of clonal B-cells detected by flow cytometry in bone marrow aspirates can predict MYD88mt status as assessed by qRT-PCR. METHODS:A total of 88 cases with IgM monoclonal paraprotein and available bone marrow immunophenotyping and MYD88 mut qRT-PCR results were retrospectively analyzed. Flow cytometry was used to identify clonal B-cell populations, and results were correlated with molecular findings. RESULTS:The absence of clonal B-cells by flow cytometry demonstrated a high negative predictive value (NPV) of 96% for MYD88mt. Conversely, the presence of a clonal B-cell population showed a positive predictive value (PPV) of 62% for detecting MYD88mt by molecular testing. CONCLUSIONS:Bone marrow immunophenotyping by flow cytometry may serve as an effective screening tool to stratify patients with IgM monoclonal paraproteinemia for MYD88mt molecular testing. Specifically, the absence of clonal B-cells strongly predicts a negative molecular result, potentially reducing unnecessary molecular analyses.