PIK3CA and cancer: Here, we provide several lines of evidence implicating an oncogenic role of nuclear p85β in PIK3CA helical domain mutant cancers: (1) knockout of p85β reduces xenograft tumor growth of PIK3CA E545K mutant cells (DLD1 E545K-only and H460), but not the PIK3CA WT cells (DLD1 WT-only) and PIK3CA H1047R mutant cells (RKO); (2) knockdown of p85β reduces the growth of a panel of PIK3CA helical domain mutant cell lines, not a panel of PIK3CA kinase domain mutant cell lines; (3) the p85β NLS mutant DLD1 knockin cells, lacking nuclear translocation of p85β, have reduced xenograft tumor growth.