AR and prostate cancer: Most CSCs may lack or under-express the differentiation molecules targeted by the mainstay cancer drugs used in the clinic, e.g., androgen receptor (targeted by ADT/enzalutamide) in prostate cancer, estrogen receptor (targeted by tamoxifen and fulvestrant) in breast cancer, RTKs (targeted by tyrosine kinase inhibitors (TKIs)) in multiple epithelial cancers, and PD-L1 (targeted by immune checkpoint inhibitors or ICIs such as Atezolizumab, Avelumab and Durvalumab) in solid tumors.