Among these claudins, the expression of claudin-1, -2, -12, and -19 were increased in colon cancer patients; mRNA expression of claudin-5, -8, -15, -17, -20, and -23 were significantly decreased in patients with colon cancer; and the expression of claudin-3, -4, -6, -7, -9, -10, -11, -14, -16, and -18 did not show distinct changes in patients with colon cancer and normal. This evidence concerns the gene CLDN5 and malignant colon neoplasm.