A scheme of myelogenous leukemia progression in time. Myelogenous leukemia progresses through four distinct phases. After an initial period of 3-5 years the abnormal cell counts rise to a relatively steady state, called the chronic phase. At this stage the disease can be diagnosed. Several years of the chronic phase where the abnormal cell count oscillates with a period of the order of months are followed by a phase characterized by oscillatory instability (the acceleration phase). Ultimately, this leads to the usually fatal acute phase with sharp increase in the abnormal cell count. This is known also as the blast crisis .