Excess of blood group B in primary myelofibrosis.

The distribution of ABO and Rhesus (D) blood groups was studied retrospectively in 40 patients with primary myelofibrosis (PMF). Only patients with a leukoerythroblastic peripheral blood, splenomegaly and marrow fibrosis in whom chronic myeloid leukemia and secondary myelofibrosis was absent were included in the study. In 14 patients (35%), PMF was preceded by another myeloproliferative disorder (polycythemia rubra vera, essential thrombocythemia or unclassified myeloproliferative disorder), while 26 patients (65%) represented agnogenic myeloid metaplasia (AMM). Comparison with Hospital and Irish blood group distribution showed a significant increase in blood group B (p less than 0.01) in PMF. This increase remained statistically significant for both the AMM and the non-AMM subgroup of PMF when each subgroup was considered separately. This finding supports previous suggestions that the various myeloproliferative disorders which proceed to myelofibrosis are a closely related group rather than a heterogeneous collection of diseases.