PIK3CA and breast cancer: Moreover, loss of function mutations in PTEN (phosphatase and tensin homolog), also demonstrated to be mutually exclusive with PIK3CA mutations in BC, and mutations in AKT1 (AKT serine/threonine kinase 1) and NF1 (neurofibromin 1) are associated with endocrine resistance and could be valuable extended assessments of these results4,8,14.