CXCR4 and monocytic leukemia: Then, patients with FAB subtypes M4 and M5 harboring monocytic leukemia cells exhibited significantly higher CXCR4 expression than patients with other FAB subtypes, consistent with the characteristics of peripheral blood hyperleukocytosis, skin damage, hepatosplenomegaly, extramedullary infiltration and a poor prognosis in patients with monocytic leukemia.