Terminal Ph1-positive monocytic crisis in chronic myeloid leukemia providing evidence for the promyelocytic origin of monocytes.

A case of Ph1-positive chronic granulocytic leukemia in described in which a terminal monocytic crisis developed. The case still was Ph1-positive at the time of the monocyte crisis. Bone marrow smears contained promyelocytes and early granulocytes, but most of the cells belonged to the monocyte series as cytochemistry disclosed. No blast cells could be detected. Cytochemically, transitions between promyelocytes and promonocytes could be demonstrated. From these findings and those from the literature it is concluded that the monocytes of the terminal crisis in our case belonged to the leukemic cell strain and that these monocytes developed from non-specific promyelocytes like granulocytes. Our observation does not provide evidence for the existence of a separate monoblast which would implicate disparity of granulocytopoiesis and monocytopoiesis already at the level of undifferentiated blast cells. This, in turn, would be equal to a re-introduction of a modified polyphyletic theory of white blood cell formation.