Different composition of the erythropoietic tissue in bone marrow, spleen and liver in myelofibrosis.

Aspirates from bone marrow, spleen and liver were analysed in 10 untreated patients with idiopathic myelofibrosis (MF). The proportion of erythroblasts was higher in the spleen and the liver than in the bone marrow. The mitotic indices of the erythropoietic precursor cells were subnormal in the extramedullary sites and significantly lower in the liver compared with the spleen. There was a "shift to the left" within the liver erythropoiesis and a significant megaloblastosis in the spleen. The same tendencies have formerly been found in patients with chronic myeloid leukemia and it is suggested that the discrepancies may be due to differences in the microenvironment of the erythropoietic cells.