Hypermethylation of the SOCS3 promoter was identified in 5 out of 19 (26.3%) PV cases, 2 out of 21 (9.5%) ET cases, 1 out of 5 (20%) PMF cases, and 9 out of 42 (21.4%) cases of secondary erythrocytosis/thrombocythemia. Here, SOCS3 is linked to essential thrombocythemia.