An advanced phase of chronic myelogenous leukemia. It is characterized by: 1. the presence of blasts in the peripheral blood or bone marrow that are at least 20% of the peripheral blood white cells or of the nucleated cells in the bone marrow respectively, or 2. an extramedullary proliferation of blasts, and/or 3. when there are large aggregates and clusters of blasts in the bone marrow biopsy specimen (adapted from WHO, 2001). The disease is blast phase chronic myelogenous leukemia, BCR-ABL1 positive (MONDO_0006115). Also known as: blast crisis, blast phase CML, blast phase chronic granulocytic leukaemia, blast phase chronic granulocytic leukemia, blast phase chronic myelocytic leukaemia, blast phase chronic myelocytic leukemia, blast phase chronic myelogenous leukaemia, blast phase chronic myelogenous leukemia.