Idelalisib is a potent and selective inhibitor of p110δ (IC50 = 8 nM) [15], and two phase I clinical trials reported asymptomatic grade 3 or greater serum transaminase elevations in 25% (n = 64) indolent non-Hodgkin lymphoma (iNHL) [21] and in 35% (n = 40) MCL [22] patients. The gene discussed is PIK3CD; the disease is mantle cell lymphoma.