Studies on the expression of genes associated with the phenomenon of apoptosis in oral squamous cell carcinoma cell lines (SCC15, SCC25, and CAL27) found that treatment with calcitriol at physiological concentrations (10–125 nmol/L) influenced programmed cell death by modulating the mRNA expression of key cell cycle and apoptotic signalling pathway regulators, such as p53, c-myc, ornithine decarboxylase (ODC), caspase-2, caspase-8, and Bax. Here, ODC1 is linked to oral cavity squamous cell carcinoma.