In this study, we examined important regulators of the PI3K pathway in primary breast carcinoma and normal breast tissue to test whether an increased expression of the PI3K pathway activator, PIK3CA, a reduced expression of the tumour suppressor, PTEN, and the presence of PIK3CA mutations in breast carcinoma tissue are associated with lymph node metastases. This evidence concerns the gene PIK3CA and breast carcinoma.