In relapsed chronic lymphocytic leukemia (CLL), idelalisib, a selective small-molecule inhibitor of p110δ, an isoform of the Class 1 PI3K catalytic subunit that is highly expressed in lymphoid cells, in combination with the CD20 monoclonal antibody rituximab, significantly improved progression-free and overall survival [9]. The gene discussed is PIK3CD; the disease is B-cell chronic lymphocytic leukemia.