[Retinoid receptors and hematologic diseases]

Acute promyelocytic leukemia is a rare disease combining a specific cell type, a bleeding diathesis and a translocation t(15;17). All trans retinoic acid is able to induce a maturation of malignant cells, up to terminal differentiation. After 2 months of treatment a complete remission is obtained without any aplastic anemia. The bleeding diathesis rapidly disappears. However relapses occur within few months due to the catabolism of retinoic acid induced by the treatment itself. A chemotherapy is generally proposed, in order to consolidate the complete remission. The combination of retinoic acid and chemotherapy has dramatically increased the probability of long term survival. The breakpoint of the translocation t(15;17) is located inside the retinoic acid receptor gene on chromosome 17. A new product is made, due to the fusion of the truncated retinoic acid receptor and a gene on chromosome 15. The hybrid product blocks the program normally performed by the retinoic acid receptor and consequently blocks the maturation of the granulocytes. Why pharmacological doses restore the impaired program is still an enigma.