Regulatory approval of the oral JAK1/JAK2 inhibitor ruxolitinib (Quintás-Cardama et al., 2010) was based on the randomized, open-label, multicenter phase III RESPONSE trial, which evaluated ruxolitinib vs. best available therapy (BAT; i.e., hydroxyurea, interferon-α, anagrelide, immunomodulators, pipobroman, and observation alone) in patients with PV who required phlebotomy to control hematocrit, had splenomegaly, and were resistant to or intolerant of hydroxyurea (Vannucchi et al., 2015). The gene discussed is JAK2; the disease is acquired polycythemia vera.