BCR::ABL1-negative MPNs, ET, PV, and MF, are MPN entities with the highest prevalence and are clonally driven by acquired mutations in the Janus kinase 2 (JAK2), calreticulin (CALR), or myeloproliferative leukemia virus (MPL) genes. The gene discussed is BCR; the disease is myeloproliferative neoplasm.