The relevance of specific mutations to human cancers is variable, with some genes (Tp53, Cdkn2a, Erbb2, Chek2, Kras and Pik3r1) harboring many alterations with COSMIC relevance while the opposite is true for other target genes (Idh1/2, Atrx, Notch1, Pten, Rb1 and Setd2). This evidence concerns the gene PIK3R1 and cancer.