Breast cancer cases with PIK3CA-activating mutations are discriminable from those without (sdis = − 0.52; p = 0.0; srand = 6.2e−6) with specific proteins (increased levels) PR, ER-alpha, MAPK_pT202_Y204, Fibronectin, AR, and GATA3 in mutated cases and Cyclin_B1, Cyclin_E1, ASNS, and HER2 being decreased. The gene discussed is ESR1; the disease is breast cancer.