['Period 3 (PER3), a circadian regulation protein, influences cell cycle, growth, and differentiation. The aim of the present study was to determine whether PER3 expression is associated with colon cancer incidence and progression.', 'PER3 expression was analyzed in the normal and cancerous tissues from patients with colon cancer by establishing a long serial analysis of gene expression (SAGE) database as well as by real-time PCR and immunohistochemistry.', 'As compared with normal tissue, a 2.8-fold decrease in PER3 mRNA levels in colon cancerous tissue was observed. Real-time PCR analysis revealed that PER3 mRNA levels in tumor tissues were lower than in normal tissues (P < 0.001) in both patients with colon tumor and those with rectal tumor. In addition, PER3 expression was related to multiple clinicopathologic factors, including tumor location, differentiation, and stage. Furthermore, the incidence of death was higher in subjects with PER3-negative tumors (P = 0.025); the estimated overall survival time was 71.5 ± 2.2 months and 58.6 ± 5.0 months in subjects with PER3-positive and PER3-negative tumors, respectively (P = 0.020).'] Is reduced expression of PER3 associated with incidence and development of colon cancer?