PDCD1 and breast cancer: Although F1/F3 combined with anti-PD-1 further hindered 4T-1 growth and metastasis, its effect was not superior to that of F1/F3 alone (Figure S3A–D), potentially due to tumor-mediated epigenetic upregulation of PD-L1 for instance, removing inhibitory DNA/histone modifications at the CD274 locus in breast cancer stem cells [61].