Identification of somatic frameshift mutations in exon 9 of the calreticulin gene (CALR) in myeloproliferative neoplasms (MPNs) in December of 2013 has been a remarkable finding. It has provided a new molecular diagnostic marker, particularly in essential thrombocythemia (ET) and primary myelofibrosis (PMF), where is the second most common altered gene after JAK2V617F. There are two main types of CALR mutants, type 1 and type 2, and there is evidence about their distinct clinical/prognostic implications, for instances, it is believed that favorable outcome might be restricted to type-1 in PMF. By using reasoned approaches, very recent publications have supported classifying the alternative mutants in type-1-like or type-2-like. If further studies confirm these results, new considerations may be taken into account in the molecular diagnosis of MPNs. This implies that precise mutation characterization must be performed and caution should be taken in screening technique selection. In this Editorial we summarize the current information regarding all this issues.
Keywords: CALR; myeloproliferative neoplasms; type-1/2-like mutations.