Abstract
Epigenetic alterations by promoter DNA hypermethylation and gene silencing in cancer have been reported over the past few decades. DNA hypermethylation has great potential to serve as a screening marker, a prognostic marker, and a therapeutic surveillance marker in cancer clinics. Some bodily fluids, such as stool or urine, were obtainable without any invasion to the body. Thus, such bodily fluids were suitable samples for high throughput cancer surveillance. Analyzing the methylation status of bodily fluids around the cancer tissue may, additionally, lead to the early detection of cancer, because several genes in cancer tissues are reported to be cancer-specifically hypermethylated. Recently, several studies that analyzed the methylation status of DNA in bodily fluids were conducted, and some of the results have potential for future development and further clinical use. In fact, a stool DNA test was approved by the U.S. Food and Drug Administration (FDA) for the screening of colorectal cancer. Another promising methylation marker has been identified in various bodily fluids for several cancers. We reviewed studies that analyzed DNA methylation in bodily fluids as a less-invasive cancer screening.
Highlights
In prior decades, many studies have reported epigenetic aberrations in cancer
Methylation status of salivary DNA is performed for early detection of head and neck squamous cell carcinoma (HNSCC)
In colorectal cancer (CRC) screening, a higher sensitivity and specificity of stool DNA tests were reported and they can be used in clinical situations
Summary
Many studies have reported epigenetic aberrations in cancer. DNA hypermethylation of the promoter region of specific genes are a major epigenetic change, where some of the cancer-specific methylation genes are tumor suppressor genes. As the first screening tool for cancer detection, ctDNA analysis is not fully appropriate; the method required to detect cancer-derived DNA alterations from ctDNA in serum or plasma uses highly technique-intensive tools, such as digital polymerase chain reaction (PCR) or generation sequencers, in which the detection level is up to 1/100,000, while prevalent tools, such as TaqMan PCR, can reach detection levels of 1/1000 [3,18] Such advanced methods cannot be performed in many laboratories around the world at present. There have been several studies, using different methods, which reported cancer specific DNA methylation in bodily fluids around the primary tumor (stool of CRC patients, urine of bladder cancer patients, etc.). All studies we reviewed focus on promoter hypermethylation, but not the methylation of other genomic regions
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