Alpelisib is an inhibitor of phosphatidylinositol-3- kinase (PI3K) with inhibitory activity predominantly against PI3Kalpha. Gain-of-function mutations in the gene encoding the catalytic alpha-subunit of PI3K (PIK3CA) lead to activation of PI3Kalpha and Akt-signaling, cellular transformation and the generation of tumors in in vitro and in vivo models.