Idelalisib (ZydeligTM; CAL-101; Gilead Sciences) is a first-in-class, highly specific, small molecule inhibitor targeting p110δ, that was indicated, in combination with rituximab, for the treatment of patients with relapsed chronic lymphocytic leukaemia (CLL) by the FDA in 2014. The gene discussed is PIK3CD; the disease is B-cell chronic lymphocytic leukemia.