Deregulated expression of the PER1, PER2 and PER3 genes in breast cancers Shou-Tung Chen1,2, Kong-Bung Choo3,

Disruption of circadian rhythm may be a risk factor in the development of breast cancer, but molecular changes in circadian rhythm controlled genes in breast cancer cells are still unexplored. We used immunohistochemical stain-ing, methylation specific PCR and direct sequencing meth-ods to analyze molecular changes in three most important genes, namely PER1, PER2 and PER3, in circadian rhythm in 55 cases of breast cancer of Taiwanese women. Our results reveal disturbances in the expression of the three period (PER) genes in most (495%) of the breast cancer-ous cells in comparison with the nearby non-cancerous cells. The PER gene deregulation is not caused by genetic mutations but most probably by methylation of the PER1 or PER2 promoter. Methylation of the PER gene pro-moters has a strong correlation with c-erbB2 expression (P 0.017). Since the circadian clock controls expression of cell-cycle related genes, we suggest that disturbances in PER gene expression may result in disruption of the control of the normal circadian clock, thus benefiting the survival of cancer cells and promoting carcinogenesis. Differential expression of circadian genes in non-cancerous and can-cerous cells may provide a molecular basis for chronother-apy of breast cancer