CALR and essential thrombocythemia: These mutations are represented by insertions or deletions, all located in exon 9.7 All mutations cause a frameshift, which lead to a unique alternative reading frame coding a novel protein C-terminus consisting of approximately 36 amino acids.5, 6, 8 Vannucchi et al.8 have successfully raised in rabbits a polyclonal antiserum against a peptide containing significant parts of the novel C-terminus of mutated CALR. With this antiserum CALR-mutated cells could be detected in formalin-fixed routinely processed BM sections of patients with ET and PMF carrying CALR mutations.