PS1471 MYELOPROLIFERATIVE NEOPLASMS IN KOREAN CHILDREN AND YOUNG ADULTS

Background: Myeloproliferative neoplasms (MPNs) are a rare, heterogeneous group of clonal hematopoietic stem cell disorders, characterized by aberrant proliferation of one or more myeloid lineages leading to an overproduction of both mature and immature cells. Three major components of classical BCR‐ABL‐negative MPNs are polycythemia vera (PV), essential thrombocythemia (ET), and primary myelofibrosis (pMF). They may be transformed to either secondary MF (sMF) or secondary acute myeloid leukemia (sAML). In addition, they can have second cancers during follow up (FU). These classical MPNs primarily occur in middle and advanced age adults, and are exceptionally rare in pediatric age. Aims: We conducted an epidemiologic study to elucidate clinical course of MPNs in children and young adults under 30 years of age focusing on disease transformation as well as thromembolism and second cancers. Methods: We analyzing data from the Health Insurance Review and Assessment Service (HIRA) database which includes almost all hospital‐based patients’ information in Korea. Results: A total of 352 patients who were diagnosed as one of the three kinds of MPNs from Jan. 2008 to Dec. 2016 (242 patients for ET, 104 for PV, and 6 for pMF) were included. Six pMF patients were excluded from further analysis. The incidence was 0.148 per 100,000 for ET and 0.064 per 100,000 for PV. Among 242 ET patients, the male‐female ratio was 119 to 123, and median age at diagnosis was 22 years (range 13–29). Four ET patients (1.65%) underwent any transformation during the study period (median FU duration 49.5 months); ET→PV (i.e., initially diagnosed ET but changed to PV later; N = 2), and ET→sMF (N = 2). Among 104 PV patients, the male‐female ratio was 96 to 8, and median age at diagnosis was 24 years (range 11–29). No PV patients were transformed into sMF during the FU period (median 45.9 months). sAML did not develop in both ET and PV patients. Solid cancers occurred in 5 ET patients and 3 PV patients. Cumulative incidence of arterial and venous thromboembolism were 6.98% and 1.71% in ET, 16.69% and 4.77% in PV, respectively. Five‐year overall survival and transformation‐free survival (to PV, MF and cancer) were 98% and 96.12% in ET, 100% and 97.29% in PV, respectively. Summary/Conclusion: This is the first population‐based epidemiologic study in Korean children and young adults with MPNs. The incidence of MPNs is very low in this age group. ET is more common than PV, whereas pMF is very rare. Transformations of ET to PV or MF occurred in a small number of patients. Considering long latency to transformation in MPNs, continuous observation is needed. In addition, second solid tumors should also be carefully observed. Further research is necessary in this patient group, including studies involving other complications such as bleeding.