Clinical characteristics, prognostic factors, and outcomes of patients with essential thrombocythemia in Japan: the JSH-MPN-R18 study.

We conducted a large-scale, nationwide retrospective study of Japanese patients who were diagnosed with essential thrombocythemia based on the diagnostic criteria in the World Health Organization classification. We investigated clinical characteristics, survival rates, and the incidence of thrombohemorrhagic events as well as risk factors for these events. A total of 1152 patients were analyzed in the present study. Median age at diagnosis was 65 years, the median platelet count was 832 × 10/L, and the positive mutation rates of JAK2V617F, CALR, and MPL were 62.8, 25.1, and 4.1%, respectively. Compared with European and American patients, Japanese patients were more likely to have cardiovascular risk factors and less likely to have systemic symptoms including palpable splenomegaly. Thrombocytosis was identified as a risk factor for hemorrhagic events and prognosis, but not for thrombotic events. The prognostic factors and risk classifications reported in Europe and the United States were generally applicable to Japanese patients. Regarding transformations, secondary myelofibrosis progressed in a time-dependent manner, but progression to acute leukemia was low in "true" ET patients. Skin cancers were less common and gastrointestinal cancers more common as secondary malignancies in Japanese patients, suggesting ethnic differences.