Only 0.32% of somatic point mutations in PU.1 are reported in hematopoietic and lymphoid tissues in the COSMIC database, (Table 2) and one recurrent somatic PU.1 mutation shown to be associated with a poor prognosis of Waldenstrom macroglobulinemia, underscoring the rarity of PU.1 somatic mutations. Here, SPI1 is linked to Waldenstrom macroglobulinemia.