The myeloproliferative neoplasms (MPN) of essential thrombocythemia (ET) and primary myelofibrosis (PMF) can be broadly molecularly characterized into four main groups according to the presence of acquired mutations in JAK2, CALR or MPL genes (all resulting in cytokine-independent proliferative signaling) or those without these mutations, termed “triple negative” (Grabek et al., 2020[5]). The gene discussed is CALR; the disease is myeloproliferative neoplasm.