CLOCK and cancer: Instead, cumulative hypermethylation at a relatively small number of 163 epiTOC2 CpGs appears to be a much better and robust mitotic age clock for adult tissues, and so we propose that measurement of DNAm at these sites in adult pre-neoplastic lesions, potentially in serum cell-free DNA [19], could provide the basis for building feasible pre-diagnostic or cancer risk assays.