JAK2 and myeloproliferative disorder: Moreover, myelofibrosis was a very common phenomenon in the bone marrow biopsy of this atypical MPN, that is, 11 of these 13 cases showing grade 2 to 3 reticulin fibrosis, which is consistent with another case series of concurrent BCR-ABL1 fusion and JAK2 V617F mutation.[11]