PIK3CA and neoplasm: In addition, some PTEN-deficient tumors are dependent on PI3Kβ signaling because depletion of PIK3CA has no impact on cell growth in three PTEN-deficient cancer cell lines, whereas inhibition of the PIK3CB isoform, responsible for encoding p110β, resulted in tumor growth suppression in vitro and in vivo (Wee et al., 2008).