Calreticulin mutations are driver mutations detected in around 20–25% of essential thrombocythemia and in 25–30% of primary myelofibrosis patients. The most recurrent mutations are type-1 (a deletion of 52 bp in the exon 9) and type-2 (an insertion of 5 bp in the exon 9). This review describes the distinct clinical features, prognosis and outcome of calreticulin mutated patients from JAK2V617F or MPL (thrombopoietin receptor) mutated patients. The subtypes of calreticulin mutations were also associated with distinct clinical characteristics. Several treatment guidelines were adapted for calreticulin-mutated patients. The mechanism by why the three driver mutations, which all activate JAK/STAT signalling pathway can trigger diseases with quite different features is still not known. The recent progress in the understanding of calreticulin mutation biology will allow the development of new target therapies with the hope to cure the disease in the next years.

(BELG J HEMATOL 2022;13(8):293–301)