A Simple Blood Test May Reveal Cancer Diseases.. Who Does It Include?

Note from the editor: This article by Dr. Sanjay Gupta is the chief medical correspondent for Horizon News. - I did not expect to feel this much anxiety; I am a neurosurgeon, and my daily work involves opening human skulls. Over the past fifty years, I have undergone blood draws dozens of times without paying much attention, as I always considered them a "routine procedure that will likely yield normal results."

But I felt that this time was different. As I watched the lab technician place identification labels on two blood tubes, I thought to myself: "This may not be a cause for concern, or it could change every detail of the next year of my life." This test is known as "Galleri," produced by a company called "Grail."

The test belongs to a new category of blood tests designed for the early detection of multiple types of cancer, and some refer to them as "liquid biopsies." The idea is both simple and brilliant: when tumors grow, most of them release parts of their DNA into the bloodstream, and thus a single blood sample can reveal those parts and potentially detect early signs of more than 50 types of cancer.

This is what my friend Katrina Verlick explained to me when she called me a few months ago. Katrina is also a neurosurgeon, and we are both nearly the same age, having spent our careers in a world reliant on imaging and certainty.

She told me that she took the test spontaneously and without prior planning, as she was in excellent health and had no symptoms at all, so the positive test result surprised her. In a subsequent scan using positron emission tomography (PET), a bright spot appeared, which she described as a bright mass "like a light bulb" in her chest.

It was a lymphatic tumor of the "Hodgkin" type, and it was discovered at such an early stage that the treating thoracic surgeon told her, in a phrase that combined humor and seriousness, that she might be one of the most "unlucky" lucky people he had ever met in his life: she is unlucky because she has cancer, but she is lucky because the doctor told her that he rarely detects tumors this small. I asked her if she thought I should also get tested, and she replied, "Do you want to discover cancer at an early stage?

For this reason, I rolled up my sleeves and found myself living that existential moment inside the blood analysis lab. A simple question and a complex answer; the numbers related to early detection are truly astonishing, as estimates suggest that routine screenings and preventive efforts have prevented about 4.75 million cancer deaths in the United States between 1975 and 2020, making it one of the greatest public health achievements of the past half-century.

But the problem lies in the following: almost all those benefits stem from just five tests, which are screenings for breast, cervical, colorectal, lung, and prostate cancers. As for the other types of cancer, such as brain, pancreatic, ovarian, most blood cancers, and dozens of other types, there is no recommended early detection test for them at all.

These types are usually discovered the old-fashioned way, that is, when a person starts to feel a slight illness or suffers from persistent pain. This means they are detected at a late stage, where treatment becomes more difficult and the chances of recovery have already diminished for the patient.

So yes, I like the idea of early cancer detection. But when I started to delve deeper into this matter, I realized that it is not that simple; appreciating the idea is one thing, and trusting the accuracy of the test is something entirely different.

As we have discussed this issue more over the past few months, my feeling of concern about that gap has increased. The problem is simply this: these tests are characterized by their accuracy in revealing the truth when their result is positive, that is, when they detect the presence of a problem.

If the "Galleri" test indicates an abnormality, the likelihood that it is a true cancerous tumor is indeed high, which is known as the "positive predictive value." But the real benefit of any test also lies in its ability to provide a truthful result when the result is negative.

So, what does a "negative result" really mean? Unexpected consequences. I spoke with Dr. Virshali Shukla, who runs an early cancer detection program specifically for firefighters in the state of Arizona, a group that has elevated cancer rates due to chronic exposure to toxins and carcinogens while on the job.

Shukla has overseen nearly 10,000 of these "liquid biopsy" tests over the past five years, but the number of cases discovered this way has not exceeded 12 cases. She told me, "The test does not detect cancer cases."

In one week, her team drew blood samples from 500 firefighters in one day, and all results came back negative. While this seems good, the problem is that none of them wanted to undergo regular routine screenings afterward, because the negative result from the "Galleri" test gave them a false sense of security.

It took Shokla and her team about two years to convince the firefighters themselves to return and undergo the screenings they had been ignoring. When they finally did, it turned out that 15 of them had cancer.

This is how I think about it now: a negative result does not mean you are completely free of disease; it only means that this specific test, on that day, did not reveal anything. If you take this result as an excuse to avoid a colonoscopy or a mammogram or any other recommended screening, you have replaced an effective screening tool with a false sense of reassurance.

The company "Grail" agrees with this view, as they explained to me in an email: "All materials directed to doctors and patients clearly state that the Galleri test is not a substitute for routine screenings, but should be used alongside those screenings." Even a positive result can have unexpected consequences, and not every cancer detected early requires early treatment, or even treatment at all.

Some tumors grow so slowly that they will not cause any problems throughout your life. If you discover a tumor of this kind, you will not have saved a life; rather, you will have initiated what doctors call a "cascade of care."

This may mean more imaging tests, more biopsies, more time in waiting rooms, and nights spent wondering if your body has let you down in some way. Despite the wonders of these new technologies, there is a disappointing reality: we simply do not have an answer to the fundamental question: do these technologies save lives?

So far, large-scale and long-term trials necessary to prove this have not been conducted. It may take decades for results of this kind to emerge.

I conducted the test despite all that. I won't claim that my decision was entirely rational, or that the weeks of waiting to know the results weren't a bit harsh.

The test was not without value, but it also did not clarify everything; it did not completely confirm that I was not sick, nor did it exempt me from undergoing the scheduled routine examinations for this year. I will not give them up as I am set to undergo a colonoscopy in conjunction with my birthday.

This experience taught me an expensive lesson (costing nearly a thousand dollars) about how to assess health risks in light of new tests and options available for evaluation. It may not be surprising that the experience also enhanced my appreciation for those traditional, unappealing tests that we have trusted for decades, such as colonoscopies and mammograms.

While no one enjoys undergoing them, they provide a benefit that the "Galleri" test is still unable to offer, which is the conclusive evidence that they save lives.