Inadequate serum TPO levels in patients with AML. (A) Relation between serum TPO levels and platelet counts in patients with ALL (squares) or AML (circles) at diagnosis. Open symbols depict patients with c-mpl^- blasts, and closed symbols depict patients with c-mpl⁺ blasts. Ellipses represent bivariate confidence regions computed in various groups: healthy controls (n = 23) and patients with aplastic anemia (n = 13), ALL (n = 42), and AML (n = 33) at diagnosis. Solid line represents the regression line computed in ALL patients after the first 2 weeks of induction chemotherapy (n = 38). Dashed lines depict the 95% confidence limits of this regression. (B) Serum TPO levels were significantly lower in patients with c-mpl⁺ AML than in patients with c-mpl^- AML or ALL. Similarly, TPO levels were lower in patients with AML with leukemic cells responding to TPO by an increase in c-fos expression than in patients with ALL or c-fos^- AML. Statistical significance was computed using one-way ANOVA.