Determination of MYD88L265P mutation fraction in IgM monoclonal gammopathies

We describe a novel method for the detection of MYD88(L265P) mutation using a competitive allele-specific polymerase chain reaction (Cast-PCR) assay. This assay has a sensitivity of 1 x 10(-3), is applicable in reactions containing very low amounts of DNA (as low as 20 pg), and allowed the detection of MYD88(L265P) somatic mutation in both tumor-derived DNA (tDNA) and cell-free DNA (cfDNA). In addition, using the Cast-PCR assay, we were able to determine the mutation allele fraction (MAF) in each tested sample. We then analyzed baseline tDNA and cfDNA samples from 163 patients (53 with immunoglobulin M monoclonal gammopathy of undetermined significance and 110 with Waldenstro euro m's macroglobulinemia [WM], of whom 54 were asymptomatic and 56 were symptomatic) and also in sequential samples of 37 patients. MAF in both cfDNA and tDNA was higher among patients with symptomatic compared with asymptomatic WM and in those with asymptomatic WM compared with those with immunoglobulin M (IgM) monoclonal gammopathy of undetermined significance. In addition, the evaluation of sequential samples showed that MAF decreased after treatment, whereas it increased in patients who relapsed or progressed to symptomatic WM. Thus, Cast-PCR is a highly sensitive, cost-effective diagnostic tool for MYD88(L265P) detection, applicable in both tDNA and cfDNA samples, that also provides a quantitative evaluation of the tumor load in patients with IgM monoclonal gammopathies.

Automated summary

We present a novel method for detecting MYD88(L265P) mutation, which has high sensitivity and can be used for detecting low amounts of DNA. This method allows for quantitative evaluation of mutation allele fraction and can be applied to tumor-derived DNA and cell-free DNA.