Acute leukemia in polycythemia vera.

Virtually every aspect concerning the occurrence of acute leukemia in polycythemia vera is controversial. However, a list of those factors believed to have importance in leukemogenesis in this disease includes: maleness, ethnic origin, the presence of myeloid metaplasia and/or early WBC precursors in the peripheral blood at the time of presentation, the influence of prolonged survival, and a possible dose-response relationship with 32P treatment. Many of the features of PV suggest that it is a malignant disease per se, with other factors (such as clones of cells, or altered host response) combining to increase the leukemogenic potential of the agents used to control the disease. It does appear that the incidence of AL in PV treated with 32P and/or x-ray is many times higher than that for PV treated with phlebotomy alone. However, overall survival for 32P-treated patients appears to be longer than that for phlebotomy treatment. Further, for both 32P and phlebotomy treatments, patients with AL do not die an an earlier age than do patients not developing this complication. Since the transformation of PV into AL has been described in more than 20 patients treated with phlebotomy alone, and in more than 30 patients treated with chemotherapy and phlebotomy, the question concerning the occurrence of AL in PV no longer appears to revolve around whether this is a function of the leukemogenicity of 32P or the effect of prolongation of survival. The occurrence of AL in multiple myeloma, lymphomas, other malignancies, and in nonmalignant diseases following treatment with myelosuppressive agents, forces one to consider the leukemogenic potential of any agent capable of suppressing the panmyelopathy of this disease, as well as the inherent tendency to AL of the "untreated" disease. Hopefully, the next decade will give us a more complete understanding of the complex interrelationships between PV, its treatment, and AL.