CLOCK and neoplasm: Mutations in circadian clock genes have been observed in tumour tissue – specifically, in colorectal cancer, breast cancer, prostate cancer and thyroid carcinoma.[54–56] The expression of DEC1 is down-regulated or absent in >50% of oesophageal cancers in man.[57] Disruption of the normal circadian cycle may be implemented on epigenetic level in tumour cells.