Cancer: soon a simple blood test to spot or follow the disease?

A simple blood test to gauge the effectiveness of a treatment against cancer or even to identify a tumor very early in the body: explored by scientists, these avenues will undoubtedly one day become a reality.

Dozens of studies are underway to demonstrate the usefulness of using a new tool, “liquid biopsy”, in monitoring patients treated for cancer.

A liquid biopsy is nothing other than a blood test which aims to search the blood of a patient for fragments of DNA from the tumor or cancer cells.

This technique has considerable advantages and many observers believe that its discovery would deserve a Nobel Prize for medicine: it is notably much less invasive than a “classic” biopsy, which takes tissues from the body.

Above all, it contains very precise information on a patient’s cancer: “the sampling of what is called “circulating DNA” aims to detect mutations, for certain types of cancer, and thus adapt treatments accordingly. », Explains Alain Thierry, director of research at the Cancer Research Institute of Montpellier (south of France), specialist in the subject.

For certain cancers such as those of the lung, where the tumors are often difficult to access, this is a real breakthrough.

The analysis of the blood of patients could also soon make it possible to monitor how a cancer reacts to treatment. “In concrete terms, after the surgical removal of a tumour, chemotherapy is often prescribed when we do not know if the patient really needs it,” notes Mr. Thierry.

In the future, the analysis of a patient’s blood may, in many cases, make it possible to administer lighter or shorter treatments, but also to detect possible recurrences.

But the liquid biopsy also conceals other potentials, certainly much more uncertain. “There is one that is dizzying: it’s early detection of cancer,” enthuses Alain Thierry.

Very expensive

Several teams and biotechs are working on it around the world. The idea: to be able to detect a tumor in an individual by taking their blood, even before symptoms appear or it is visible on an X-ray.

“Technologically, it is much more complicated than monitoring cancer because it requires large-scale analysis of DNA mutations but also other specific markers, while not knowing in advance what we are looking for”, describes François-Clément Bidard, oncologist at the Curie Institute in Paris, head of the laboratory of circulating tumor biomarkers.

Recently, the results of a study by the American biotech Grail were particularly noticed: in their trial, a blood test made it possible to detect cancers in individuals aged 50 and over who were a priori healthy. More than 6,600 people took the test. There was a suspicion of cancer for 92 of them. In the end, 35 actually had confirmed cancer during the year and 57 people therefore mistakenly believed that they had one.

But the test made it possible to detect 9 cancers which would probably not have been detected by early conventional screening.

However, the results are very mixed and it will probably take years to improve the reliability of these tests, which are already marketed in the United States.

And, even reliable, these tests will still raise certain questions, warns François-Clément Bidard.

“One of them is the cost, this type of sequencing being extremely expensive. Another subject is the possible “over-diagnosis” induced by these tests, because a certain number of cancers detected have in fact an extremely slow evolution and do not necessarily call for treatment”, he explains.

It will also be necessary to prove that these tests represent a notable progress compared to those which are in force today.

“We still have well-established cancer screening strategies today”, but “the participation rate is only 40% at best” in these screening tests offered by Health Insurance, recalls Professor Fabrice Barlesi, director general of the Gustave-Roussy cancer center, in the Paris region, who does not, however, exclude that the tests by blood test serve one day as a “complement”.