Clonal architecture and evolutionary history of Waldenstrom's macroglobulinemia at the single-cell level

To provide insight into the subclonal architecture and cooependency patterns of the alterations in Waldenstro'' m's macroglobulinemia (WM), we performed single-cell mutational and protein profiling of eight patients. A custom panel was designed to screen for mutations and copy number alterations at the single-cell level in samples taken from patients at diagnosis (n=5) or at disease progression (n=3). Results showed that in asymptomatic WM at diagnosis, MYD88L26 5 P was the predominant clonal alteration; other events, if present, were secondary and subclonal to MYD88L265P . In symptomatic WM, clonal diversity was more evident, uncovering combinations of alterations that synergized to promote clonal expansion and dominance. At disease progression, a dominant clone was observed, sometimes accompanied by other less complex minor clones, which could be consistent with a clonal selection process. Clonal diversity was also reduced, probably due to the effect of treatment. Finally, we combined protein expression with mutational analysis to map somatic genotype with the immunophenotype. Our findings provide a comprehensiv e view of the clonality of tumor populations in WM and how clonal complexity can evolv e and impact disease progression.