Phases of Chronic Myelogenous Leukemia

Unlike most cancers, chronic myelogenous leukemia (CML) is classified into phases rather than stages, based partly on the percentage of immature white blood cells (blasts) in peripheral blood and bone marrow. A complete blood count with differential, peripheral blood smear, and bone marrow analysis are used to determine the phase. The 3 phases of CML, as defined by the World Health Organization (WHO),^{[1, 2]}are listed below.

Table. Phases of Chronic Myelogenous Leukemia (Open Table in a new window)

CML phase	WHO definition
Chronic stable phase	Blasts < 10% in peripheral blood and bone marrow
Accelerated phase	Blasts comprising 10-19% of white blood cells (WBCs) in peripheral blood and/or nucleated bone marrow cells Peripheral blood myeloblasts and promyelocytes combined ≥30% Peripheral blood basophils ≥20% Persistent thrombocytopenia (< 100 × 10 ⁹/L) unrelated to therapy or persistent thrombocytosis (> 1000 × 10 ⁹/L) unresponsive to therapy Increasing WBC counts and spleen size unresponsive to therapy Additional clonal cytogenetic abnormalities in Philadelphia chromosome–positive (Ph+) cells
Blast crisis	Blasts ≥ 20% of peripheral blood WBCs or nucleated bone marrow cells Extramedullary blast proliferation Large foci or clusters of blasts on bone marrow biopsy

National Comprehensive Cancer Network guidelines recommend against using WHO definitions for accelerated or blast phase CML, and instead recommend Modified MD Anderson Cancer Center (MDACC) criteria for accelerated phase CML and International Bone Marrow Transplant Registry (IBMTR) criteria for blast phase.^[1]

MDACC criteria for accelerated phase CML are as follows^[1]: