CALR and essential thrombocythemia: While most Ph-neg MPN patients harbor mutually exclusive somatic mutations in the genes of JAK2 (exon 12 or 14), CALR (calreticulin–CALR protein; frameshift mutation in exon 9), or the thrombopoietin receptor MPL (exon 10) [1], 10–15% of PMF and ET patients are termed to have triple-negative MPN because they do not show any of these so-called driver mutations [2].