Endogenous megakaryocytic colonies underline association between megakaryocytes and calreticulin mutations in essential thrombocythemia

Calreticulin ( CALR ) mutations occur in 20%–25% of myeloproliferative neoplasms (MPN).[1][1],[2][2] At least 40 CALR mutations have been reported to date, all located in exon 9. The most frequent CALR mutations are a 52-bp deletion (type 1) and a 5-bp insertion (type 2). Expression of type 1 CALR