At MPN, we observed a cytokine cluster in the minimal 5q deleted genomic region compassing nine genes (IL4, CSF2, TSLP, IL3, IL5, IL9, IL13, IL12B, and SPRY4) that are part of the JAK-STAT signaling pathway associated with proliferation and differentiation of the hematopoietic compartment. The gene discussed is IL9; the disease is myeloproliferative neoplasm.