PIK3CA and cancer: Specifically, we used BAY-1082439, a highly selective PI3K inhibitor of the PI3K 110α and 110β isoforms and which is currently undergoing phase I clinical trials in patients with advanced cancer (ClinicalTrials.gov Identifier NCT01728311), in conjunction with Pik3ca or Pik3cb knockout in two MDR cancer cell lines, KB-C2 and H460/MX80, which overexpress the transporters P-gp and BCRP, respectively.