In order to investigate this possible cause–effect relationship, we evaluated WASP protein expression in cell lines derived from BCR–ABL1-negative leukemia (HL-60, Jurkat, SKW6.4, THP-1 and U937) and BCR–ABL1-positive CML patients (K562, BV173, LAMA-84 and KCL22). This evidence concerns the gene ABL1 and leukemia.