PIK3CD and mantle cell lymphoma: However, the first p110δ isoform-selective PI3K inhibitor, idelalisib (GS-1101), with notable results in indolent non-Hodgkin lymphoma[5] and chronic lymphocytic leukemia,[6] showed modest responses in patients with MCL.[7] Moreover, it has been postulated that the increased expression of PI3K p110α isoform in MCL particularly at relapse might play a role in MCL progression,[8] supporting the use of pan-PI3K inhibitors.