SFRP4 and head and neck squamous cell carcinoma: Since 1997, our research group has extensively published on Wnt signalling and the role of secreted frizzled related protein (sFRP4) and its associated domains, cysteine rich domain (CRD) and netrin-like domain (NLD) as an antiangiogenic protein in various cancers such as brain, breast, ovary, prostate, mesothelioma, including HNSCC CSCs and now recently in reproductive CSCs of breast, prostate and ovary [122,175,176,177,178,179,180,181,182,183,184,185,186,187].