Evaluation of the need for cytoreduction and its potential carcinogenicity in children and young adults with myeloproliferative neoplasms.

Myeloproliferative neoplasms are rare at a young age, and few reports have described the disease characteristics and outcomes in this group. This study aimed to elucidate the clinical course of essential thrombocythemia (ET) and polycythemia vera (PV) in children and young adults aged <39 years focusing on thromboembolic events (TE) and second primary malignancies (SPMs). A total of 990 patients who were diagnosed from 2008 to 2017 were included by analyzing the Health Insurance Review and Assessment Service database in Korea. The incidence was 2.53 per 1,000,000 for ET (643 patients; 276 male patients; median 31 years) and 1.37 per 1,000,000 for PV (347 patients; 309 male patients; median 32 years). Three ET patients developed secondary acute myelogenous leukemia and three developed secondary myelofibrosis. The 5-year cumulative incidence of TE was 14.2% in ET and 21.3% in PV. Thus, the incidence was higher in PV; in particular, arterial TE (ATE) was evidently higher in PV than in ET. The 5-year cumulative incidence of SPMs was 2.5% in ET and 2.6% in PV. While the use of both aspirin and hydroxyurea reduced the incidence of ATE, hydroxyurea significantly increased the incidence of SPMs. The incidence of ET and PV was very low, and ET was more common than PV in children and young adults. The high incidence of TE in young patients suggests the importance of thrombosis prevention. However, hydroxyurea appears to increase the incidence of SPMs; therefore, the risks and benefits should be considered.