30 November 2012

Blood test for all types of cancer: one more step

American scientists have proposed a genetic method for diagnosing all types of cancer

Copper news based on the materials of Science: A Step Towards a Universal Cancer Blood TestResearchers from the Johns Hopkins University School of Medicine predict the introduction into medical practice in the coming years of a universal non-invasive genetic test for oncological diseases by blood analysis, which allows diagnosing all types of cancer at the earliest stage.

In any case, the results of their latest work on the identification of tumor DNA fragments freely circulating in the bloodstream on the basis of chromosomal disorders reflected by them, the authors believe, makes this prospect more realistic. The work (Leary et al., Detection of Chromosomal Alterations in the Circulation of Cancer Patients with Whole-Genome Sequencing) is published in the journal Science Translational Medicine.

Existing developments in this area are aimed at detecting DNA fragments of cancer cells in the blood, the source of which were certain types of neoplasms, that is, the genetic background of the search object is known in advance. Experts from Johns Hopkins University have set themselves the task of identifying circulating tumor DNA regardless of the type of cancer, that is, with an unknown genetic background.

At the same time, the authors were based on the assumption that all cancer cells, without exception, contain multiple chromosomal abnormalities that distinguish them from healthy cells. This fact was confirmed after a genome-wide analysis of extracellular DNA isolated from the blood plasma of ten patients with advanced stage of breast and rectal cancer, as well as ten members of the control group, using the method of massive parallel sequencing.

It turned out that the blood of all cancer patients contained freely circulating extracellular DNA, indicating chromosomal mutations, while in healthy people such structural changes in extracellular DNA were completely absent. The level of tumor DNA in the blood of cancer patients ranged from 1.4 to 47.9 percent.

The color highlights mutant areas on identical chromosomes that have entered the blood from breast cancer cells.
Illustration provided by Cambridge University

In some patients, during the study of the detected chromosomal abnormalities, an increase in the number of copies of two oncogenes ERBB2 and CDK6 was revealed, which, according to the authors, also speaks in favor of the proposed method – an immediate start of therapy will be possible, no time will be spent on conducting and waiting for the results of a biopsy.

So far, the method of searching for tumor DNA among a huge number of healthy DNA cells circulating in the blood is very expensive and takes a lot of time – several thousand dollars were spent on each patient, and it took a month to perform all the procedures. However, the authors believe that it is very promising, as it allows detecting the presence of less than 0.1 percent of defective DNA in blood samples and diagnosing cancer at the earliest stages. In addition, in the near future, such an analysis will become much more accessible, since the cost of sequencing is constantly falling, and the speed is increasing.

According to Carlos Caldas, who is engaged in similar research at Cambridge University, testing for oncological diseases by blood analysis based on genetics methods may appear in widespread medical practice in the next five to ten years.

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