In this study, the expression profiles of eight circadian clock genes (PER1, PER2, PER3, CRY1, CRY2, CKIε, CLOCK, and BMAL1) of cancerous and noncancerous tissues from 29 GC patients were investigated using real-time quantitative reverse-transcriptase polymerase chain reaction and validated through immunohistochemical analysis. Here, PER1 is linked to gastric cancer.