Chronic myelomonocytic leukemia: from biology to therapy.

Chronic myelomonocytic leukemia represents a distinct myelodysplastic syndrome in which an excess of monocytes is observed both in the blood and bone marrow of the patients. Whereas diagnosis is relatively easy, therapeutic design and efficacy is difficult and no treatment has to date provided complete or significant partial response. In vitro data suggest that the growth and differentiation of myelomonocytic progenitors may be altered inasmuch as monocytic or granulo-macrophagic colonies show spontaneous growth. Different entities may be observed: the childhood form, Juvenile Chronic Myelomonocytic Leukemia (JCML) shows in vitro a typical pattern with constitutive growth of only macrophagic colonies and hypersensitivity to GM-CSF; in the adult form at least two patterns may be observed one close to the JCML form and one more heterogeneous with absence of GM-CSF sensitivity and spontaneous growth of both CFU-GM and CFU-M colonies. Chemotherapy reduces all myeloid colonies in vitro whereas retinoic acid has a selective effect on monocytic colonies with a concomitant increase of CFU-G colonies forwarding an explanation for the correction of pancytopenia observed in some patients. Recent analysis of altered molecular pathways in this disease suggest a common disruption of intracellular signalling pathways namely the Ras pathway and targetting for drugs with may selectively control or inhibit a constitutive activation may forward novel therapeutic perspectives.