Blast Phase of Myeloproliferative Neoplasm Resembles Acute Myeloid Leukemia, Myelodysplasia-Related, in Clinical Presentation, Cytogenetic Pattern, and Genomic Profile, and Often Undergoes Reversion to Second Chronic Phase Status After Induction Chemotherapy

Context.— BCR::ABL-negative myeloproliferative neoplasm (MPN) has a prolonged clinical course, and some cases eventually undergo transformation to blast phase; its pathogenesis remains to be elucidated. Objective.— To evaluate the clinicopathologic characteristics of MPN in blast phase. Design.— The study aimed to retrospectively analyze the clinical and laboratory data of 24 MPN cases. Results.— Median latency to blast phase was 48 months (range, 7–384 months). Complex karyotypes were seen in 12 of the 24 cases (50%). Overall, 16 cases (66.7%) exhibited high allele burdens of MPN driver mutations along with increased blasts, consistent with linear clonal evolution, whereas the remainder (8; 33.3%) showed loss or partial loss of the driver mutation, suggestive of a parallel evolution. Additional mutations were noted in 23 cases (100%), including TP53 mutations in 10 of 24 cases (41.7%). Following chemotherapy, 15 of the 24 patients (62.5%) reverted to a second chronic phase while retaining or regaining MPN driver mutations and losing blast-related mutations, although 9 of the 15 patients (60%) later died of disease progression. Median overall survival was 10 months (CI, 4.6–15.4), with those harboring complex karyotypes demonstrating decreased survival (6 versus 29 months; P = .004). Conclusions.— MPN blast phase resembles acute myeloid leukemia, myelodysplasia-related, in cytogenetic pattern, mutation profile, and clinical outcome. Two patterns of clonal evolution are inferred by dynamic analysis of mutation profiles: linear and parallel evolutions. Although overall survival was dismal, 62.5% of our cases achieved second chronic phase, and they showed better survival than those without second chronic phase.