The current study involves 100 MMB-treated patients (median age 66 years; 58% males) from the Mayo Clinic who were enrolled between 20 November 2009 and 10 November 2010; 64 patients had primary, 22 post-polycythemia vera, and 14 post-essential thrombocythemia MF; 73 (73%) harbored JAK2 mutations, 16 (16%) CALR, 7 MPL, and 4 were “triple-negative”; among the 16 CALR-mutated cases, 13 were type 1/like. Here, CALR is linked to medullomyoblastoma with myogenic differentiation.