Studies investigating combination treatment with lapatinib and ipatasertib in the PIK3CA-mut HER2+ breast cancer cell lines revealed that inhibition of both the MAPK and PI3K pathways is critical to inhibit proliferation in HER2+ breast cancer cell lines, and that expression levels of p4EBP1 were correlated with the antiproliferative effects of the inhibitors (Figs. 3a, 5a). This evidence concerns the gene PIK3CA and breast carcinoma.