Indeed, an attentive cytomorphologic examination of BM (cellularity, ratio erythropoiesis/granulopoiesis, specific features of MKs, BM fiber content) is essential in the discussion about differential diagnosis and in some difficult or atypical BCR::ABL1-negative MPN cases, above all in “triple negative” MPN. This evidence concerns the gene BCR and myeloproliferative neoplasm.