In a retrospective study of 100 patients with chronic MPN and either PV or essential thrombocythemia, mutations in IDH1/2 or SF3B1 were associated with myelofibrotic transformation and mutations in ASXL1, TP53, SRSF2, IDH1/2, and RUNX1 were associated with transformation to MPN-BP19. The gene discussed is TP53; the disease is myeloproliferative neoplasm.