Will this Grail of Oncology ever be found? Doctors dream of being able to establish an early diagnosis of cancers by a simple blood test: by analyzing the traces left in the bloodstream by tumor cells (DNA, proteins, or even micro-RNA), or the circulating tumor cells themselves.
These tests, if they were efficient and available, would offer an easy, non-invasive, large-scale means of detecting cancers very early – before their local spread and, above all, before their dissemination in the body in the form of metastases. . However, we know that the earlier a cancer is detected and treated, the greater the chances of a cure.
Over the past ten years, thousands of studies have been published on the subject. The latest, in the review Nature Communications of July 21, suggests that this dream is no longer a utopia. According to the international team behind this work, a blood test detected five types of cancer (stomach, esophagus, colon, lung and liver) in asymptomatic subjects. This, up to four years before the diagnosis of their tumor, by conventional imaging methods.
The principle of this test, called PanSeer? It analyzes the circulating tumor DNA released into the blood by tumor cells (because they die or secrete it). But this test does not analyze the sequence of this tumor DNA, looking for mutations. More subtly, he maps out a chemical marking that marks out the DNA molecule: “methylation”, which corresponds to the addition of “methyl” groups (CH3). These come to fix themselves on a small word, frequent in the large book of DNA. They bind to the letter “cytosine” (C), when it is followed by the letter “guanine” (G) (this word is named “CpG”). This DNA methylation is an essential mechanism for controlling gene activity – through an “epigenetic” process. DNA methylation profiles vary according to the type of cells (kidney, liver, skin, brain, etc.) and according to age.
A multi-billion dollar hope
But how do you distinguish the DNA of tumor cells from that of healthy cells? “Previous studies have compared DNA methylation profiles in cancerous or healthy tissue. Verdict: some methylation profiles seem specifically associated with different types of cancer ”, explains Professor Thierry Frébourg, specialist in cancer genetics at the Rouen University Hospital (Inserm), who did not participate in this study.
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