Several studies have indicated PTEN, PIK3CA, and AKT1 mutations to be mutually exclusive (i.e. not co-occurring in the same tumor tissue sample) in individual tumors [5, 13, 17], suggesting that mutational activation of the phosphatidylinositol 3-kinase pathway by any one of these means is biologically equivalent. This evidence concerns the gene PIK3CA and neoplasm.