CLOCK and cancer: The Horvath clock has strong correlation with the chronological age but no association with the CRC risk; it appears to result from an intrinsic aging process that is not affected substantially by cell type/composition, cell proliferation, or environmental factors; while the Hannum, PhenoAge, and EpiTOC clocks exhibit differences between the CRC risk groups, they may better measure not only the internal clock mechanism of cell division but also exposure to phenotypic epi-mutagens during cancer progression.