There have been six epigenome-wide association studies (EWAS) for breast cancer risk using blood DNA from prospective cohorts published thus far, and the only consistent finding is a global loss of methylation observed in breast cancer cases compared with controls, with no individual CpG sites passing validation across studies. In contrast, a more successful approach has been the identification of EWAS signatures of cancer risk factors such as smoking, body mass index, age and alcohol use with numerous validated CpG sites. These signatures may be used as a molecular test to quantify cancer risk associated with these factors. It is clear from the larger EWAS of risk exposures that similar-sized large collaborative studies may be needed to robustly identify DNA methylation signatures of breast cancer risk.
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