New DNA Based Blood Test Detects Early Stage Cancers

Highlights:

• Failure of early detection of cancers leads to high mortality and morbidity.
• New blood based test detects early stage cancers with an overall success of 62%.
• Researchers claim that smokers and women with inherited breast cancer mutations are the ones who would benefit the most from the new development.

While cancer cases are rising at an alarming rate every year, early detection of the cancers is still a relatively difficult phenomenon. In fact, much of the morbidity and mortality in human cancer is related to the late diagnosis of this disease, where surgical and pharmacologic therapies are less effective. A recent study conducted at the Johns Hopkins Kimmel Cancer Center, reported a test that uses small amounts of cancer specific DNA in blood to detect early stage cancers. The study is published in the journal Science Translational Medicine.
How is the cancer detected?
The test is based on isolating cell free tumor DNA (ctDNA) from blood. Apart from DNA which is present in our cells, some DNA is present outside the cells, in the bloodstream, which is called free circulating DNA (cfDNA). Similarly, in tumor patients, cfDNA includes ctDNA that breaks away from the primary tumor and enter the bloodstream and is circulating.

In normal healthy individuals there is a low level of cfDNA due to immune cell clearance. However, in tumor patients, the ctDNA is present in higher levels in the blood as they evade immune cells. This, if detected and sequenced will give information on the type of primary tumor present in the body.

How specific is the test?

Until recently, the clinical utility of ctDNA for the detection of cancer was not well explored due to limited sensitivity of current technology. Low levels of ctDNA present in blood and unknown driver mutations were the key problems.

The research team at John Hopkins has developed an approach called targeted error correction sequencing (TEC-Seq) that allows ultrasensitive direct evaluation of the tumor causing mutations in circulating cell-free DNA. This is based on deep sequencing or reading of the DNA which means more than 30,000 reads. Scientists claim that the test can distinguish accurately between tumor-derived DNA and other altered DNA that are mistaken for cancer biomarkers This helps in greatly reducing false positives.

To develop the test, scientists obtained 200 blood samples of patients with breast, lung, colorectal and ovarian cancer The test screened the samples for 58 genes that were widely linked to the cancers. Overall, the test was successful in detecting 62% of stage I and II cancers. Also, 44 healthy individuals were also tested and none of them showed positive results for the test.

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However, the test needs to be validated in a larger cohort to understand its efficacy.

Advantages of the test

• Blood collection for cancer detection is non-invasive and can be done on spot. Useful in situations where collecting a solid tumor sample is too invasive, or if there is not enough sample to detect cancer.
• Gives clear indication of presence and type of tumor at any given point of time.
• Beneficial for high-risk smokers for whom CT scans for lung cancer often lead to false positives.
• Also provides an easy and convenient form of testing for women with known hereditary breast cancer mutations.

Reference:

1. Phallen, J., Sausen, M., Adleff, V., Leal, A., Hruban, C., White, J., Anagnostou, V., Fiksel, J., Cristiano, S., Papp, E., Speir, S., Reinert, T., Orntoft, M., Woodward, B., Murphy, D., Parpart-Li, S., Riley, D., Nesselbush, M., Sengamalay, N., Georgiadis, A., Li, Q., Madsen, M., Mortensen, F., Huiskens, J., Punt, C., van Grieken, N., Fijneman, R., Meijer, G., Husain, H., Scharpf, R., Diaz, L., Jones, S., Angiuoli, S., Ørntoft, T., Nielsen, H., Andersen, C. and Velculescu, V. (2017). Direct detection of early-stage cancers using circulating tumor DNA. Science Translational Medicine, 9(403), p.eaan2415.

Source-Medindia