PDCD1 and malignant colon neoplasm: Intrigued by the intrinsic immune suppressive microenvironment and high frequency of immune evasion of colon cancer (18, 19), we postulate that PSEN1 may contribute to the regulation of PD-1/PD-L1 signaling in colon cancer, and thus investigate the relationship between PSEN1 and PD-L1 translocation.