Laboratory signs detected in the 5 cases of PV occurring after CML were as follows: red blood cell (RBC) increase and HCT increase in 2/5 cases (5, 24); WBC, Hb level and PTL increase in 1/5 cases (18); HCT and Hb increase in 1/5 (53), whereas HCT and Hb increase were associated with low erythropoietin (EPO) level in 1/5 (52). The gene discussed is EPO; the disease is acquired polycythemia vera.