Liquid biopsies are today used mainly after a cancer diagnosis, to profile tumour DNA or monitor recurrence. A study published in Cell Genomics by researchers at Oxford Population Health and the University of Toronto asks a more ambitious question: whether blood drawn from apparently healthy people carries molecular traces of cancers that will not be diagnosed for years. The answer, at least for prostate cancer, appears to be yes.
The team analysed stored blood from 491 participants in the Ontario Health Study, all cancer-free at the time of collection, some of whom later developed breast or prostate cancer. Using highly sensitive profiling of DNA methylation, the chemical tags that switch genes on and off, they found that prostate cancer produced the strongest early signal, through methylation changes in regulatory regions called silencers, identifying high-risk individuals five to eight years before diagnosis.
Breast cancer proved harder to detect, though methylation changes in enhancer regions still separated women at higher and lower risk between one and a half and eight years ahead of diagnosis. With no population-wide screening programme currently in place for prostate cancer, the authors suggest such tests could eventually direct proactive surveillance towards those who need it while sparing low-risk individuals unnecessary investigation, a significant step for a disease where late detection drives mortality.