CML is characterized by three phases or stages. The first stage is called the Chronic Phase. The vast majority of patients (85% to 90%) are diagnosed while in the Chronic Phase. Very often, individuals in the Chronic Phase have no or few symptoms and are diagnosed through a routine blood test. Some people in the Chronic Phase experience symptoms such as fatigue, shortness of breath, feeling of fullness or pain in the upper left side of the abdomen (due to enlarged spleen), weight loss, night sweats and anemia. Typical features of Chronic Phase are: elevated white blood cell (WBC) count; normal or high platelet count; increased basophil count; sometimes increased eosinophil count; and, most importantly, fewer than 15% myeloblasts. In the Chronic Phase, as in all three phases of CML, the marrow is usually hypercellular at diagnosis.
With modern TKI treatment, the vast majority of treated patients do not progress beyond the Chronic Phase.