DPP4 and rectal cancer: Expression level of CD26 and MMP1 in CRC specimens from TCGA was analyzed at GEPIA (http://gepia2.cancer-pku.cn/#index (accessed on 23 November 2021)), which showed that CD26 was positively correlated with MMP1 level in colon and rectum cancer (R = 0.18, p = 0.00067).