To evaluate the clinical impact of a constitutively-activated PI3K pathway in patients with PIK3CA, AKT, PIK3R1 mutation, and PTEN homozygous deletion or mutations, we retrospectively reanalyzed a large and unbiased clinical dataset of anti-HER2 therapies in the HER2+ metastatic or recurrent breast cancer patients24 (Supplementary Table S1). This evidence concerns the gene PIK3R1 and breast cancer.