MYD88^L265P Detection in IgM Monoclonal Gammopathies: Methodological Considerations for Routine Implementation

Area of Science:

• Hematology
• Molecular Diagnostics
• Oncology

Background:

• MYD88^L265P is a key biomarker in IgM monoclonal gammopathies, predicting prognosis and therapy response.
• Allele-specific quantitative PCR (ASqPCR) is the standard for MYD88^L265P detection, but droplet digital PCR (ddPCR) shows promise for screening and minimal residual disease (MRD) monitoring.

Purpose of the Study:

• To compare the sensitivity and concordance of ASqPCR and ddPCR for MYD88^L265P detection across various sample types.
• To evaluate the suitability of ddPCR for minimal residual disease monitoring in IgM monoclonal gammopathies.

Main Methods:

• Comparison of ASqPCR and ddPCR for MYD88^L265P detection.
• Analysis of bone marrow (BM), peripheral blood (PB), sorted/unsorted CD19+ cells, and plasma cell-free DNA (cfDNA).
• Assessment of concordance and sensitivity between the two PCR methods.

Main Results:

• Good concordance (74%) between ASqPCR and ddPCR, particularly in BM samples.
• ddPCR showed higher sensitivity, detecting mutations missed by ASqPCR, especially in low-burden samples like PB and cfDNA.
• MYD88^L265P detection in PB using ASqPCR was suboptimal for screening and MRD analysis.

Conclusions:

• ddPCR is a sensitive and feasible method for MYD88^L265P detection across diverse specimen types, including cfDNA.
• CD19+ cell selection is unnecessary with ddPCR due to its high sensitivity.
• Distinct MYD88^L265P levels between Waldenström Macroglobulinemia and monoclonal gammopathy of undetermined significance warrant further investigation into progression risk.