Using <i>in situ</i> hybridization, the expression of key clock genes, including period circadian protein homolog (<i>Per</i>) 1 and 2, cryptochrome 1 (<i>Cry1</i>), circadian locomoter output cycles protein kaput (<i>Clock</i>), brain and muscle ARNT-like protein 1 (<i>Bmal1</i>) and casein kinase 1ε (<i>CK1</i>ε) were retrospectively examined in 51 cases of colorectal carcinoma and 10 cases of adenoma.