Myeloproliferative neoplasms (MPNs) are a major subgroup of chronic myeloid neoplasms, alongside myelodysplastic syndromes (MDS), MDS/MPN overlap syndromes, and myeloid/lymphoid neoplasms, with eosinophilia associated with recurrent PDGFRA, PDGFRB, FGFR1, or PCM1-JAK2 rearrangements. Here, PCM1 is linked to myelodysplastic syndrome.