Although, in an early study, CSF3R mutations had been reported in 59% of patients with aCML and CNL (25, 36), further studies did not confirm this high frequency, and it is now believed that CSF3R-mutated aCML is in fact rare (19, 37). This evidence concerns the gene CSF3R and atypical chronic myeloid leukemia, BCR-ABL1 negative.