Molecular Genetic Markers and Clinical Characteristics of Essential Thrombocythemia

Abstract

Background & Aims. The presence of different molecular genetic markers of clonality (mutations in JAK2, MPL, CALR) or their absence (triple negative status, TN) in essential thrombocythemia (ET) indicates a biological heterogeneity of the disease and can determine its clinical forms. The aim was to evaluate the association of molecular genetic markers with the clinical form and the prognosis of ET. Materials & Methods. We analyzed the data of 240 patients with ET at the age of 20-91 years (median age 58.7 years), who were observed in the Russian Research Institute of Hematology and Transfusiology from 1999 to 2016 (median observation period 37.2 months). Results. The JAK2V617F (JAK2+) mutation was found in 182 (75.9 %) of 240 patients. CALR (CALR+) mutations were found in 30 (12.5 %): type 1 (CALP7+) mutations in 13/30 (43.3 %) and type 2 (CALR2+) in 17/30 (56.7 %). MPL (MPL+) mutations were found in only 2 (0.8 %) of 240 patients. None of the mutations were detected in 26 (10.8 %) of 240 patients (TN status). Significantly higher platelet counts were observed in CALP7+ and CALR2+ subgroups during the primary diagnosis of ET compared with JAK2+ and TN groups. The mean platelet counts were 1252 * 10<sup>9</sup>/L for CALR2+ and 1079 * 10<sup>9</sup>/L for CALP7+ vs 841 * 10<sup>9</sup>/L (p < 0.001; p = 0.06) and 775 * 10<sup>9</sup>/L (p < 0.001; p = 0.04) for JAK2+ and TN, respectively. Thrombosis was diagnosed in 50 (27.4 %) of 182 patients of the JAK2+ subgroup, in 8 (30.7 %) of the 26 patients of the TN subgroup, and in 2 (18.2 %) of 11 patients of the CALP7+ subgroup. No thrombosis was found in the CALR2+ and MPL+ subgroups (p < 0.001). In general, the CALP7+ status was characterized as the most favorable in terms of prognosis (5-year overall survival rate of 100 %), compared to the least favorable TN status (5-year overall survival rate of 85 %). Conclusion. Mutations in the CALR gene were characterized by a more favorable prognosis in comparison with JAK2+and TN, as well as a decrease in the risk and frequency of thrombosis, despite higher platelet counts. TN-status of ET was associated with unfavorable prognosis.