In the RESPONSE-2 open-label phase IIIb study, efficacy and safety of ruxolitinib versus BAT were assessed in 149 PV patients without palpable splenomegaly resistant or intolerant to HU; BAT included HU (49% of subjects) and IFN or PEG-IFN (13% of subjects). The gene discussed is IFNA1; the disease is acquired polycythemia vera.