Numerous studies have shown that vitamin D elevates the expression of genes engaged in DNA damage repair including p53, proliferating cell nuclear antigen (PCNA), and breast cancer 1 (BRCA1) in breast cancer cells [123], ATM, recombinant DNA repair protein (RAD50) [147], and growth arrest and DNA damage-inducible α (GADD45α) in ovarian cancer cells and squamous cell carcinoma (SCC) [148,149]. Here, PCNA is linked to squamous cell carcinoma.