Serum thrombopoietin and erythropoietin levels in patients with acute promyelocytic leukaemia during all-trans retinoic acid treatment

Endogenous serum thrombopoietin (TPO) and various cytokines including eryth ropoietin (EPO), interleukin (IL)-3, IL-6, IL-11, granulocyte-colony stimul ating factor (G-CSF), granulocyte-macrophage-colony stimulating factor (GM- CSF) and stem cell factor (SCF) levels were measured in five patients with acute promyelocytic leukaemia (APL) during all-trans retinoic acid (RA) tre atment. During differentiation-inducing therapy, platelet counts slowly inc reased and reached a peak, between days 29 and 46 (median day 35). Serum TP O levels increased parallel to the increasing platelet counts and reached a maximum level during the first 10-20d of all-trans RA treatment, The circu lating TPO levels then decreased in inverse correlation to the platelet cou nts. These unique changes in serum TPO levels revealed that TPO levels were not regulated by platelet or megakaryocyte mass in patients with APL durin g differentiation-inducing therapy, and it would appear that TPO levels are directly regulated by all-trans RA during the first 10-20d of treatment. I n addition. the change in circulating EPO levels and reticulocyte counts we re similar to that of the TPO levels and platelet counts during all-trans R A treatment, suggesting a close relationship between TPO and EPO signalling .