PER1 and colorectal cancer: We used quantitative real-time polymerase chain reaction (qRT-PCR) to identify the expression levels of CLOCK, BMAL1, PER1, PER2, PER3, CRY1, CRY2, CSKN1E, TIM, TIPIN, Cyclin-D1, and WEE1. We observed a downregulation of core clock, as well as of clock-controlled gene mRNA expression levels in both liver metastases and colorectal cancer.