Novel CALR somatic mutations in essential thrombocythaemia

Essential thrombocythaemia (ET), primary myelofibrosis (PMF), and polycythaemia vera (PV) are Philadelphia-negative (Ph-neg) classical myeloproliferative neoplasms (MPN). Mutations in the Calreticulin gene (CALR) were discovered in both JAK2- and MPL-negative MPN patients. CALR mutations were found in about 20–25% of ET. 63 CALR mutations were described in ET. We retrospectively analysed a total of 212 consecutive ET patients diagnosed and followed-up between 2006 and 2014. All mutational analyses were performed on DNA from bone marrow or peripheral blood samples at diagnosis. CALR exon 9 mutations were detected by PCR fragment analysis and Sanger sequencing. In 212 ET patients, mutational frequencies were 51·4% (109/212) for JAK2, 28·3% (60/212) for CALR and 3·8% (8/212) for MPL, while 16·5% (35/212) of cases were ‘triple-negative’. CALR mutational frequency rose to 63·1% in both JAK2V617F and MPLW515 wild-type cases (60/95): 38 were type 1 (63·3%), 12 type 2 (20%), 3 type 3 (5%), 1 type 14 (1·7%) and 6 cases (10%) showed new mutations, all generating a + 1 base-pair frame-shift able to replace the canonical C-terminal by a new protein sequence and not described in COSMIC catalogue as of March 2015. The 6 novel mutations were mainly associated with female gender (5/6) and older age (4/6), with an average platelet count of 834 (range 659–1070) × 109/l. CALR mutation analysis can thus be a useful additional diagnostic tool to achieve an accurate diagnosis for patients with ET who lack JAK2V617F and MPLW515 mutations,