Given that there were contradictory findings regarding the effect of vitamin D on PC risk and survival and that supplementation of calcium and vitamin D, for example, increased the risk of serrated polyps, important precursors of colorectal cancer, in an RCT [12,85], it is important to elucidate the specific role of vitamin D/VDR signaling in the different stages of PC—initiation, progression, maintenance, and metastasis. The gene discussed is VDR; the disease is pachyonychia congenita.