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Cancer diagnosis through blood test

Cancer diagnosis through blood test

Cancer patients or their family usually wish that the cancer was detected in its early stages, to improve any chances of successful treatment. More than 14 million people are newly diagnosed with cancer worldwide each year. It is well established that many deaths in human cancer are related to the late diagnosis of this disease, where surgical and pharmacological therapies are less effective. 

Scientists at the John Hopkins Kimmel Cancer Centre have developed a new blood test that can reveal if a person is suffering from cancer before any symptoms have appeared. The study published in the Science Translational Medicine journal, describes an ultrasensitive test which can detect small DNA pieces released into the bloodstream from dying tumour cells. 


Scientists have discovered that dying tumour cells release small pieces of their DNA into the bloodstream. These pieces are called cell-free circulating tumour DNA (ctDNA).

      (Image Source: National cancer Institute)

The team developed a method called Targeted error correction sequencing (TEC-Seq) for specific and sensitive detection of alterations in gene sequences associated with cancer. The genes sequenced in this case were cell-free DNA (cfDNA) released from the dying tumour cells. They analysed plasma samples of 244 patients, out of which 44 were from healthy individuals, while the remaining 200 were from cancer patients at various stages. It was reported that the blood test properly detected breast, colon, lung and ovarian cancer. 

There were no false positives in the 44 people who did not have cancer. “You don’t want to go screening people for hallmark (cancer) mutations unless you absolutely know that when you find it, that there is a tumour there and that it is a tumour that needs to be treated,” says Wyndham Wilson of the National Cancer Institute, who was not involved in the study. Sometimes, early-stage tumours or precancerous growths just go away as they are attacked by the immune system or because they don’t thrive for other reasons.

“There is a lot of excitement about liquid biopsies, but most of that has been in late-stage cancer or in individuals where you already know what to look for,” said Dr. Victor Velculescu, professor at the Johns Hopkins Kimmel Cancer Centre. “The surprising result is that we can find a high fraction of early-stage patients having alterations in their blood,” said Velculescu. While the test detected cancer in more than half of the patients with stage I cancer, it was more accurate in detection of late-stage cancers. However, the goal is to detect cancer in its earliest stages when it is the easiest to treat. 

While this test shows some promise, it has to advance further before it can be used in clinics. The test will need to improve on its accuracy since it missed cancer detection in some of the samples in the study. It will also have to be tried in larger groups of patients, and patients with different cancers. The first goal would be to try it in people at high risk of cancer but no symptoms yet, such as smokers, or people with cancer-causing gene mutations like BRCA mutations. It is important to study such tests in large groups of people who have not had cancer diagnosed, to see if it can truly be used to screen asymptomatic people for cancer. 

Cancer screening is often a tricky issue. However this blood test may potentially become a standard detection tool for early-diagnosis of cancer. 


Phallen, J., Sausen, M., Adleff, V., Leal, A., Hruban, C., White, J., … & Speir, S. (2017). Direct detection of early-stage cancers using circulating tumor DNA. Science translational medicine, 9(403), eaan2415.

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