PDCD1 and breast cancer: Wan et al. found that disruption of the metadherin (MTDH)-SND1 complex sensitizes breast cancer cells to replication stress-induced apoptosis (16, 17), and Shen et al. demonstrated that disruption of the MTDH-SND1 complex by small-molecule inhibitors or compounds enhances the sensitivity of cancer cells to anti-programmed cell death protein 1 therapy, thus suppressing breast cancer progression and metastasis (13, 14), but it remains unclear whether SND1 regulates mitophagy.