Cytogenetic analysis, FISH, and a lack of typical myeloproliferative neoplasia rearrangements (BCR-ABL, PDGFRA, PDGFRB, FGFR1, and PCM1-JAK2) and mutations (JAK2, CALR, and MPL) are necessary to confirm the diagnosis of aCML. The gene discussed is PCM1; the disease is atypical chronic myeloid leukemia, BCR-ABL1 negative.