Q: Does MCED testing concern all types of cancer?
Dr. Delaloge: The Galleri test is based on full profiling of DNA methylation. This allows for early diagnosis of cancer even before it can be seen on imaging tests. The issue with these tests is that they aren’t that good at early diagnosis of the most common types of cancer (breast, colorectal, cervical, etc.) for which we already have more efficient means such as the fecal immunochemical test for colorectal cancer, mammography, HPV testing, and so on.
These blood tests would thus not be aimed at replacing routine screening but rather at screening asymptomatic individuals or those with nonspecific signs for cancers for which we have few or no screening measures and which are on the rise, such as deep tumors and cancer diagnosed at a late stage, namely pancreas, bile duct, ovarian, esophageal, lung, stomach, etc.
The results from the studies published are promising, but others are underway to confirm the benefit of these MCEDs. The challenge is to identify cancer at an early stage, at a stage where it will be easier to cure the patient and control its growth using treatments that are less onerous for the patient and that have fewer aftereffects but not at the expense of a massive increase in overdiagnosis, as seen with prostate-specific antigen levels in prostate cancer a few years ago!
Q: What would be the focus of these MCED tests?
Dr. Delaloge: We must be alert to the risk for the market development of MCED tests. For now, they are mostly, especially the Galleri test, developed in the general population to screen for types of cancer that could not be detected in any other way but also because it’s the most financially beneficial situation. The designers want to position themselves in the general population, regardless of whether this means they’ll have to test hundreds of people to find one for whom the test is beneficial. What’s more, developing tests in isolation, without considering their place in ad hoc treatment pathways, is not realistic. It’s likely that some of these tests will be marketed within the next 10 years, but the health care systems destined to receive them are not remotely ready to do so.
Q: An even more recent publication, from late July 2023, is even more exciting in relation to early detection of lung cancer using circulating DNA sequencing. What are your thoughts on it?
Dr. Delaloge: Initially overtaken by other technologies in favor of MCED approaches, DNA sequencing as a technique to detect somatic mutations seems to have reentered the competition with this new-generation research. The authors published some very interesting results, especially for stage I lung cancer with a very high sensitivity of 75%. [Editor’s note: A machine-learning model using genome-wide mutational profiles combined with other features and followed by CT imaging detected more than 90% of patients with lung cancer, including those with stage I and II disease.]
This research illustrates the difficulty of providing high performance while covering a broad range of cancers. Here, the good results mainly concern lung cancer. Researchers and health care authorities must be alert to ensuring that MCED tests prove themselves in terms of sensitivity and specificity in responding to a medical need and in their impact on specific mortality. This craze for MCED tests must not hinder the development of “single-cancer” technologies that may be much better for detecting specific cancers. This recent publication is interesting in this respect, because this sequencing test seems to be particularly good at detecting lung cancer.