CLDN18 and colorectal carcinoma: Within specific pathologic subtypes of CRC, CLDN18 expression has been reported to be higher: In signet-ring-type CRC, CLDN18 expression was reported at 37.5% while 27.8% of serrated adenocarcinomas expressed CLDN18 (n = 16 and n = 36, respectively) [159,162].