Phenotypic correlation in PV included levels of IL-12 with hematocrit; IL-1b, IL-2, IL-7, FGF-β, and HGF with leukocytosis; and IFN-α and IFN-γ with thrombocytosis, MIP-1β with survival in multivariate analysis. The gene discussed is IL1B; the disease is acquired polycythemia vera.