In February 2022, the data of Cancer Incidence and Mortality in China, 2016 published by the National Cancer Center showed that in 2016, the number of cancer cases in China was 4.064 million, including 2.375 million cases of lung cancer, colon cancer, stomach cancer, liver cancer, esophageal cancer and pancreatic cancer, accounting for 58.4% of the annual incidence of cancer in China, and 72.9% of the total deaths in China. According to the requirements of "cancer prevention and treatment project" in the Opinions of the State Council on the Implementation of Healthy China Action in July 2019, we advocate active prevention of cancer, promote early screening, early diagnosis and early treatment, orderly expand the scope of cancer screening, and reduce the incidence rate and mortality of cancer. Therefore, strengthening cancer screening and early diagnosis and treatment work, achieving a continuous decrease in cancer mortality rate, early screening and prevention are key. At present, methylation gene testing, a new tool in early screening of tumors, can assist in early screening and is a new method for early cancer detection and prognosis monitoring.

So, what is methylation gene testing? What is its significance? Now let's briefly understand the relevant knowledge about methylation gene detection.

Methylation

Concept: Methylation is a chemical modification process that involves adding a methyl group (- CH3) to certain substances (such as proteins, DNA, amino acids).

DNA methylation

Concept: DNA methylation refers to the methylation of the 5-carbon atom of cytosine (C). After DNA replication, under the action of DNA methylase, the methyl group of S-adenosylmethionine (SAM) molecule is transferred to the 5-carbon atom of the C residue in the DNA molecule.

The clinical significance of methylation detection

Methylation is extremely common in organisms and is essential in a series of important processes such as substance synthesis, transcriptional regulation, and protein activity expression. DNA methylation is one of the parameters that regulate transcription. Prior to gene mutations, it can shut down the activity of certain genes, while demethylation induces gene reactivation and expression. DNA methylation occurs in the early stages of cancer, so researchers can screen for specific gene DNA methylation levels in the early stages of tumor development.

The characteristics and advantages of methylation detection

1) Comprehensive, unaffected by lesion location, age, and gender, longitudinal evaluation of tumor evolution

2) Safe, non-invasive examination, no trauma or side effects

3) Early, high incidence cancer early signals

4) Accurate, high sensitivity, and strong specificity

5) Convenient, most peripheral blood is extracted without the need for special preparation before testing

Methods for methylation detection

There are many methylation detection methods, and currently the most widely used detection method in clinical practice is based on fluorescence quantitative PCR detection technology. Simple and fast, with a short reporting cycle, high sensitivity, and strong specificity. Taking colorectal cancer as an example, let's briefly introduce the methylation detection of the Septin9 gene in the colon.

The main function of the Septin9 gene is related to cell apoptosis and division. Methylation of the Septin9 gene can lead to abnormal cell division and carcinogenesis. The principle and method of its methylation detection are shown in the following figure.

The possibility of colorectal cancer can be determined by detecting abnormal methylation of free Septin9 in the peripheral blood of the subject through fluorescence quantitative PCR. The advantage of its detection method is that patients have high compliance, and genetic testing can be performed by extracting peripheral blood, providing patients with an additional non-invasive diagnostic method for colorectal cancer. However, there are also limitations to the detection methods, such as the possibility of false negative results due to the sensitivity and specificity of the technology and reagents. Secondly, there is a high requirement for blood samples, and patients need to have a low-fat diet one week before the examination to avoid the occurrence of fatty blood, etc.

Determination of normal and abnormal values in methylation detection results

Extract free DNA from the sample of the test subject, amplify it using fluorescence PCR technology, and determine the positivity based on the CT value of the amplification curve:

The detection result Ct ≤ threshold, and the detection result is judged as positive

Test result Ct>threshold, test result interpreted as negative

Normal reference value: negative

The postoperative test result was positive, indicating the presence of small metastases. It is recommended to conduct relevant clinical examinations for further diagnosis. The follow-up test result is positive, indicating the possibility of recurrence or metastasis. It is recommended to conduct relevant clinical examinations for further diagnosis. The test result is negative, indicating that no methylation of a certain gene has been detected.

In summary, methylation detection for early cancer is receiving increasing attention due to its advantages, and methylation detection technology has become a new tool for precise diagnosis and treatment of cancer and early screening of tumors.