How can a single blood draw detect cancer early in disease progression?
The National Cancer Institute estimates 1,735,350 new cases of cancers with mortality exceeding 600,000 this year in the US alone. It is therefore imperative to find an early detection system and effective treatment of these cancers to help ease the mortality rate.
Early detection refers to measures that can be taken to diagnose cancer as early as possible when the disease is easiest to treat. These measures include annual screens such as mammograms, pap smears, and colonoscopies given to populations that are more susceptible to these forms of cancers. Other measures include identifying changes in the skin, such as atypical moles or suspicious lesions. But often, signs of cancer are undetectable and symptoms are unnoticeable for most of the population.
Cancer is often thought to originate as a mutation in the DNA that causes a cell to malfunction and no longer abide by the processes that regulate normal cell function. However, other factors that control the switching of genes on and off have taken a front row in cancer research. Epigenetic processes that control gene expression consist of DNA methylation, chromatin remodeling, histone modification, and non-coding RNA mechanisms. Disruption of epigenetic processes can lead to altered gene function and malignant cellular transformation. One of the most striking features of cancer cells is the pattern in which DNA methylation is altered as compared to normal cells. Like a fingerprint, altered DNA methylation sites can identify specific cancers.
Of recent, liquid biopsies have rapidly gained prominence in the detection of cancers by looking for cell-free cancer-derived DNA in the blood. Consequently, the rarity of cancer-derived DNA in the early onset of the disease poses a substantial issue for detecting DNA mutations within the blood. However, researchers at Princess Margaret Cancer Centre turned to analyzing large-scale epigenetic alterations of cell-free DNA in the blood as a means of early detection and classification of cancers.
By determining the epigenetic alterations of the methylation sites in a variety of cancers, the researchers were able to identify a specific DNA methylation profile for each cancer. Using this information along with a big data approach, they applied machine learning to create classifiers that could detect these methylation changes in very small quantities of circulating cell-free DNA found in diseased blood samples. This approach allowed for the identification of seven specific cancer types (lung, pancreatic, colorectal, breast, bladder, and kidney) within blood samples.
Although further validation is needed, this study reveals a minimally invasive cancer detection system, whereby a single blood draw allows for the detection of specific cancers. Using epigenetics, a tumor-specific methylation pattern can be used as a biomarker for disease detection in the blood. This system has the potential to allow early detection of cancers and reveal an accurate diagnosis of the cancer type leading to treatments early in disease development.
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Shen SY et al. (2018) Sensitive Tumour Detection and Classification Using Plasma Cell-Free DNA Methylomes. Nature 563(7732): 579-583.