PDCD1 and breast cancer: Tfh cells can be positively (e.g., breast cancer, colon cancer, pancreatic ductal adenocarcinoma) or negatively (e.g., hepatocellular carcinoma) associated with the long-term survival of patients through releasing CXCL-13, PD-1, CXCR-5, ICOS, and BCL6 as well as interacting with B cells and CD8+ Tc cells [32–35, 51].