BCR and atypical chronic myeloid leukemia, BCR-ABL1 negative: As early findings consisted chiefly of isolated case reports or small case series, CNL was born of an era of being defined primarily by what it was not: by excluding basophilia, monocytosis, or a BCR-ABL fusion, it could be distinguished from chronic myeloid leukemia (CML), atypical chronic myeloid leukemia (aCML), and chronic myelomonocytic leukemia (CMML).