ARID1A and breast neoplasm: MutSigCV analysis identified several Cancer Gene Census (CGC) genes (http://cancer.sanger.ac.uk/census/) as having significant roles in the development/progression of AYA tumors; PIK3CA and TP53 were prominent in breast tumors, and PIK3CA, KRAS, TP53, and ARID1A in ovarian tumors (Figure 1), all of which are also frequently mutated in non-AYA breast and ovarian tumors [12, 16, 26-28].