PIK3CD and breast cancer: It has also been observed that IRS4 induces resistance to trastuzumab and lapatinib, two treatments directed against HER2+ breast cancer cells, because it is involved directly in the hyperactivation of the PI3K/Akt/mTOR pathway, which is ultimately responsible for this resistance, as shown in previous studies; thus, IRS4 is a promising therapeutic target for these types of tumours that are resistant to treatment [125, 126].