PTEN and cancer: Highlighting the importance of STAG2 as a cancer gene, in 2014 The Cancer Genome Atlas identified STAG2 as one of only 12 genes that are significantly mutated in four or more human cancer types (the others were TP53, PIK3CA, PTEN, RB1, KRAS, NRAS, BRAF, CDKN2A, FBXW7, ARID1A and KMT2D; [16]).