DNA mutations "give out" cancer in the early stages
The new blood test has already been tested
Yulia Vorobyova, Vesti
Over the past few years, researchers have created many new methods for diagnosing oncological diseases. The new tests, among other things, are aimed at detecting cancer by blood analysis. For example, Russian scientists have learned to diagnose cancer by detecting certain cancer marker proteins in blood plasma, and their Japanese colleagues are looking for tumor cell microRNAs in patients' blood - this method helps to detect 13 forms of cancer at once.
A new diagnostic method, also based on a blood test, was presented by specialists from the Sidney Kimmel Cancer Center at Johns Hopkins Hospital (USA). Their test is aimed at identifying tiny sections of DNA specific to cancer cells. The innovation of the approach is that researchers can distinguish the DNA of tumor cells from other biomarkers that can be mistaken for a sign of a malignant neoplasm.
The accuracy of this diagnosis was ensured by previous studies, during which experts studied genetic mutations found in samples of cancerous tumors. The team found that at least 82% of these mutations correlate with changes in the blood of patients who had those tumors removed.
When developing the new test, scientists focused on 58 genes that, as previously proven, are associated with specific types of cancer. At the same time, the main difficulty was to distinguish mutations caused by cancer from other genetic changes that are also present in human blood and belong to normal inherited DNA variations, or appear as a result of errors in cell division.
In addition, with such a diagnosis, scientists can be confused by so-called germ mutations, which are really changes in DNA, but occur as a result of normal changes in the body and are not associated with cancer.
Taking into account all these factors, the researchers developed a test based on a special type of genomic sequencing – a "targeted error correction sequence". This method is based on deep ordering: each "letter" of the DNA code is read 30 thousand times.
"We are trying to find a needle in a haystack, so when we detect a DNA change, we want to make sure that this is exactly what we are looking for," explains the head of the work, Professor Victor Velculescu.
Such work, covering more than 80 thousand DNA base pairs, can potentially be very expensive, but, according to the authors, sequencing technology is becoming cheaper today. In addition, further work will help reduce the number of DNA fragments that need to be checked.
The new technique has already been tested in the USA, Denmark and the Netherlands: 200 patients with various stages of cancer took part in it. Tumor tissue samples were taken from them, as well as blood tests.
The results showed that the new point identification helps to detect lung, ovarian, breast cancer, as well as colorectal cancer (this is a collective concept for cancer of various parts of the colon and rectum) at the earliest stages.
Using the new method, these types of cancer were detected in patients with an average accuracy of 62%, and at the first or second stage of the disease.
At the same time, the accuracy of detecting colorectal cancer at various stages was more than 80%, lung cancer – 69%, ovarian cancer – 75%, and breast cancer – 57%.
At the same time, in 44 blood samples of healthy patients, the test did not reveal a single mutation indicating cancer.
"This study shows that the detection of cancer in the early stages, based on the search for DNA changes in the blood, is possible. Our high–precision sequencing method is promising for achieving this goal," adds Velculescu.
But despite these encouraging results, the new diagnostic method has yet to be tested with the participation of more patients, the authors of the development emphasize.
More detailed scientific work can be found in the publication Science Translational Medicine.
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30.08.2017