Occurrence of acute leukaemia in myeloproliferative disorders.

In a series of 306 cases of myeloproliferative disorders followed over a period of 21 years, 18 cases of well-documented acute leukaemia were encountered. Leukaemias were either acute myeloblastic or myelomonocytic and occurred from 6 months to 20 years after the initial diagnosis. Onset was relatively abrupt and the course rapidly fatal with with a median survival of 4 weeks. Due to the prolonged preleukaemic phase, it was possible to carry out a variety of clinical and laboratory observations. While no consistent features were noted, dysplastic haemopoiesis, a fall in leucocyte alkaline phosphatase activity, presence of Pelger-Hüet anomaly and other abnormalities suggest a disturbance in granulocytic maturation. These findings suggest that, following an initial injury to a pleuripotential haemopoietic stem cell, a prolonged 'latent' period occurs and, due to exposure to additional injurious agents or to a lack of cell regulating factors, acute leukaemia develops.