BCR and chronic myelogenous leukemia, BCR-ABL1 positive: Chronic myeloid leukemia (CML) is classified into three subtypes based on the <i>BCR</i> breakpoint, the rarest of which is micro <i>BCR::ABL1</i> (also known as e19a2 <i>BCR::ABL1</i>), which encodes a P230 fusion protein.