Two Novel Monoallelic Calreticulin Mutations in a Patient With Essential Thrombocythemia.

Recently, mutations have been identified in the calreticulin (CALR) gene in JAK2 or myeloproliferative leukemia negative patients with myeloproliferative neoplasm. A 49-year-old male patient with incidental thrombocytosis was investigated for CALR mutation by direct sequencing method. The patient carried two novel monoallelic somatic mutations, the L367fs*52 and the p.R368W in the CALR gen, which resulted in a novel C-terminal sequence. The absent endoplasmatic reticulum retention signal in the mutant CALR results in an altered subcellular localization of the mutant protein. The new positively charged C-terminal domain has an importance for oncogenicity, effecting different signaling pathways, activating the cytokine-independent growth of the cells and down-regulating the apoptotic signaling. But the new, alternative C-terminal domain offers an opportunity for immunologic therapy as it represents a cancer-specific epitope.