A 50-year-old male presents with anemia and gingival bleeding for 6 months. Physical examination shows anemic appearance with hepatosplenomegaly. Hemoglobin (Hb) is 50g/L, white blood cell (WBC) count is 3.4×10<sup>9</sup>/L, and platelets (PLT) are 6×10<sup>9</sup>/L. Blood smear shows nucleated red blood cells. Mean corpuscular volume (MCV) and mean corpuscular hemoglobin concentration (MCHC) are normal. The most likely diagnosis is: