PDCD4 and breast cancer: HER2 activation downregulates PDCD4 through the MAPK and PI3K/AKT pathways (Cai et al., 2022), and overexpression of PDCD4 was reported to promote apoptosis in breast cancer cell lines in the presence of the HER2 inhibitor trastuzumab (Afonja et al., 2004; Cai et al., 2022).