Chronic Phase Chronic Myeloid Leukemia, Philadelphia Chromosome Positive, BCR-ABL1 Positive

**Semantic type:** Neoplastic Process

**Definition:** A phase of chronic myeloid leukemia, Philadelphia chromosome positive, BCR-ABL1 positive in which the peripheral blood smear shows leukocytosis with neutrophils in different stages of maturation, less than 2% blasts, and normal or increased platelet count. Most patients have mild anemia. The bone marrow is hypercellular due to increased numbers of neutrophils and their precursors, and blasts usually account for fewer than 5% of the marrow cells. Megakaryocytes are smaller than normal and have hypolobated nuclei. The spleen is enlarged due to infiltration of the cords of the red pulp by granulocytes.