Based on the currently available body of work on the protein expression of claudins in colorectal cancer, CLDN1, CLDN2, CLDN4, and CLDN18 have all been reported to be expressed in CRC [27,28,29,30,31,32,33,34,37,46,56,57,58,59,60,61,62,63,73,74,75,80,81,93,96,152,153,160,161,162,163,164]. This evidence concerns the gene CLDN1 and colorectal cancer.