extracting blood
Brittany Hambleton
Brittany Hambleton
December 11, 2023 ·  4 min read

Researchers say blood test can detect cancer years before symptoms

This article was originally published in August 2020 and has since been updated.

There are over two hundred types of cancer, which can affect many different parts of the body. More than one million people in the United States are diagnosed with cancer annually, and cancer accounts for thirteen percent of all deaths globally every year, about 8.8 million people [1].

Early detection is the best way to prevent individuals from dying of cancer, because the earlier abnormal tissue or cancer is found, the easier it is to treat. This means that detecting cancer even before symptoms appear is crucial, since, by the time a patient experiences symptoms, cancer may already be fairly advanced [2].

There are several different types of screening tests that can be performed to detect for specific cancers, including colonoscopies, mammograms, and pap tests, to name a few [3].

Recently, researchers in China have developed a cancer blood test that they say can detect the presence of the disease up to four years before symptoms appear [4].

Cancer Blood Test

The test, called PanSeer, is a non-invasive blood test that has the ability to detect cancer four years earlier than a conventional blood test diagnosis, the researchers say. During trials, the team was able to detect cancer in 95 percent of individuals who had no symptoms, but later received a diagnosis.

The researchers used blood plasma samples that had been collected from individuals between 2007 and 2014. 414 samples were used from participants who remained cancer-free within five years after the sample was taken, 191 samples were used from participants who were diagnosed with stomach, colorectal, liver, lung or oesophageal cancer within four years after the blood test, and 223 samples came from biobanks of patients who had already been diagnosed with one of those five cancers.

The test screened particular regions of DNA found in blood plasma for methyl groups that are often present in tumour DNA. The techniques the team used allowed them to pick up even very small levels of this type of DNA.

They then used a type of artificial intelligence called machine learning algorithms to determine if any DNA found circulating in the blood was shed by these tumours, by looking for the presence of the aforementioned methyl groups.

The results of the test demonstrated that PanSeer detected cancer in 88 percent of participants who had already been diagnosed, and 95 percent of patients who were not diagnosed but later developed cancer. The test identified participants without cancer 96 percent of the time [4].

Early Detection Decreases Cancer Mortality

In their report, which is published in the journal Nature Communications, the researchers explain that early detection allows tumors to be removed or treated with milder drug regimens, thereby increasing the likelihood of patient survival.

According to the team’s research, the five-year survival rate of patients whose cancer is diagnosed at an early stage is 91 percent, while those who are diagnosed in the late stages of the disease have a survival rate of about 26 percent [5].

Circulation DNA in blood plasma has recently been receiving a lot of attention as a promising biomarker for early cancer detection, however much of the research in this area has focused on detecting cancer in patients who have already been diagnosed. 

What is exciting about this research is that it’s one of the first to show that cancers could be detected before patients showed any indication of symptoms [4].


While very exciting, the research does have a few limitations. The sample size was relatively small and storage was not optimal so the team has expressed some concern over possible contamination. The test also does not identify which specific cancer the individual has, only that they have it.

Despite these limitations, Dr Eric Klein of Cleveland Clinic’s Taussig Cancer Institute, who has conducted his own research on the use of liquid biopsies to detect cancer, is encouraged by the results, stating that there are currently no effective cancer screening paradigms for early detection.

“This is an exciting study which provides further confirmation that methylation-based assays can detect cell-free circulating tumour DNA and may form the basis for new screening tests that detect cancer at early stages,” he said [4].

Samantha Harrison, a senior early diagnosis manager at Cancer Research UK, is also encouraged by the results, but says that they must now be replicated in a larger study.

As more work is done in this area, it is possible that a cancer blood test may become more and more common, helping doctors to diagnose patients earlier and therefore significantly increasing their chance of survival.


  1. Cancer Facts.” Cancer Research
  2. Cancer Screening.” Cancer
  3. Screening Tests.” National Cancer Institute
  4. Researchers say blood test can detect cancer years before symptoms.” The Guardian. Nicola Davis. July 2020
  5. Non-invasive early detection of cancer four years before conventional diagnosis using a blood test.” Nature. Xingdong Chen, et al. July 21, 2020.