SIgM levels are selectively increased in patients who progress after ibrutinib therapy. Expression of sIgM was measured before therapy and after ibrutinib therapy discontinuation (n = 13). SIgM levels are shown as fold change relative to pretherapy set to 1 (A) and as MFI values (B). Red lines/dots represent progressed patients. Blue lines/dots represent patients who did not progress. The dashed line in panel B represents the cutoff used in this series to discriminate CLL with high and low sIgM expression. The statistical difference was calculated using the Mann-Whitney U-test.