Vitamin D is an important fat-soluble vitamin, and the vitamin D signaling pathway is known to be involved in the regulation of cancer cell differentiation.14 Therefore, we tested the expression of several proteins that have key roles in the vitamin D signaling pathway (Fig. 1e) under pH 7.4 and 6.8, and found that VDR expression in each cell line was significantly decreased under acidosis (Fig. 1f, g). This evidence concerns the gene VDR and cancer.