骨髄増殖性腫瘍（MPN）の分類不能：変異の状況と「分類不能」の管理

Myeloproliferative neoplasm-unclassifiable (MPN-U) is a heterogenous subtype of Philadelphia-chromosome negative (Ph-) MPN that comprises 5-20% of Ph- MPN cases. Given the clinical and molecular variability of presentation, there are no clear data regarding risk stratification and management of MPN-U. In this review, we aim to summarize the current evidence regarding MPN-U with regards to diagnosis, risk stratification, and treatment approaches.

Current diagnostic criteria require exclusion of other chronic myeloid malignancies along with identifying the typical pathologic findings of an MPN in order to diagnose MPN-U. While there are not dedicated prognostic scores regarding thrombotic risk and survival specifically for MPN-U, phenotype-agnostic scores may have utility. In addition, the Dynamic International Prognostic Scoring System (DIPSS)+ score has demonstrated that it can identify higher-risk MPN-U. There are no consensus treatment recommendations available for MPN-U.

When considering management of MPN-U, for patients in the cellular phase, we consider cytoreduction in patients identified as high-risk, for fibrotic-phase disease, we consider JAK inhibition for splenomegaly/constitutional symptoms and allogeneic transplantation for higher-risk patients, and for accelerated/blast-phase disease we employ hypomethylating-agent based approaches with the intent of allogeneic transplant for eligible patients.