A simple blood test may detect cancers.. Who does this category include?

Editor's Note: This article is written by Dr. Sanjay Gupta, the chief medical correspondent for Ofoq News. - I did not expect to feel this much stress. I am a neurosurgeon, and my daily work involves opening human skulls. Over the past 50 years, I've had my blood drawn dozens of times without paying much attention, always considering it a "routine procedure with likely normal results."

But I felt that things were different this time. While I was watching the laboratory technician placing identification labels on two tubes of blood, I thought to myself: “This may not be a cause for concern, or it may change every detail of the next year of my life.” This test is known as Gallery, and is produced by a company called Grail.

The test belongs to a new class of blood tests for early detection of multiple types of cancer, and some call them “liquid biopsies.” The idea is both simple and ingenious: when tumors grow, most of them release parts of their DNA into the bloodstream, and a single blood sample can detect those parts, and perhaps detect early indicators of the presence of more than 50 types of cancer.

This is what my friend Katrina Ferlick explained to me when she contacted me a few months ago. Katrina is also a neurosurgeon, we are both about the same age, and have spent our careers in a world of radiology and certainty.

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

It was Hodgkin's lymphoma, discovered so early that her thoracic surgeon told her, both jokingly and seriously, that she might be one of the most "unlucky" people he'd ever met: unlucky to have cancer, but lucky because the doctor told her he rarely saw tumors this small. I asked her if she thought I should get tested too, and she replied, “Do you want to catch your cancer at an early stage?

For this reason, I rolled up my sleeves and found myself experiencing that existential moment inside the blood analysis laboratory. A simple question, a complex answer. The numbers related to early detection are truly staggering. It is estimated that routine screening and prevention efforts have prevented about 4.75 million cancer deaths in the United States between 1975 and 2020, constituting one of the greatest public health achievements of the past half-century.

But the problem lies in the following: Almost all of these benefits result from only five tests, which are tests to detect breast, cervical, colorectal, lung, and prostate cancers. As for the rest of the types of cancer, such as brain, pancreatic, ovarian, most blood cancers, and dozens of other types, there is no recommended early detection test at all.

These types are usually discovered in the old traditional way, that is, when a person begins to feel a little unwell or suffers from pain that does not go away. This means that it is detected at a late stage, when it becomes more difficult to treat and the chances of recovery are already diminished for the patient.

So yeah, I like the idea of ​​catching cancer early. But when I started to dig deeper into this matter, I realized that it is not that simple. Approval of the idea is one thing, but confidence in the accuracy of the examination is quite another.

The more we've addressed this issue over the past few months, the more concerned I've become about that gap. The problem is simply this: These tests are most accurate in revealing the truth when their result is positive, that is, when they detect the presence of a problem.

If the Gallery test indicates something abnormal, the probability that it is an actual cancer is already high, which is known as the “positive predictive value.” But the real benefit of any test also lies in its ability to give an honest result when the result is negative.

So, what does a “negative result” really mean? Unexpected Consequences I contacted Dr. Virshali Shukla, who runs an early cancer detection program for firefighters in the US state of Arizona, a group that has high rates of cancer as a result of chronic exposure to toxins and carcinogens on the job.

Shukla has performed nearly 10,000 of these “liquid biopsy” tests over the past five years, but only a dozen cases have been detected this way. “The test does not detect cancer,” she told me.

One week, her team drew blood samples from 500 firefighters in one day, and all the results came back negative. Although this seemed good, the problem was that none of them wanted to undergo the usual regular examinations after that, because the negative “Gallery” test result gave them a false sense of security.

It took Shukla and her team about two years to convince the firefighters themselves to go back and perform the checks they had been ignoring. When they finally did, 15 of them were found to have cancer.

This is how I think about it now: A negative result doesn't mean you're completely disease-free, it just means that that particular test, on that day, didn't reveal anything. If you use this finding as an excuse to avoid a colonoscopy, mammogram, or other recommended screening, you have replaced an effective screening tool with a false sense of reassurance.

Grail agrees, telling me in an email: “All materials for doctors and patients clearly state that the Gallery test is not a substitute for routine screening, but should be used in addition to those screenings.” Even a positive result may have unexpected consequences, and not every cancer detected early may require 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 type, you will not have saved a life, but rather you will have begun what doctors call a “cascade of care.”

This may mean more scans, more biopsies, more time in waiting rooms, and nights wondering if your body has somehow failed you. As wonderful as these new technologies are, there is a disappointing truth: we simply do not have an answer to the fundamental question: Do these technologies save lives?

So far, the large, long-term trials needed to prove this have not been conducted. It may take decades for results of this kind to appear.

A Lesson in Risk Assessment I took the test after all. I won't pretend that my decision was completely rational, or that the weeks of waiting to find out the results weren't a little brutal.

The test was not useless, but it did not clarify everything either. It did not confirm that I was completely free of the disease, and it did not exempt me from undergoing the periodic examinations scheduled for this year. I will not give it up as I am scheduled to undergo a colonoscopy to coincide with my birthday.

This experience gave me an expensive lesson (costing about $1,000) in how to assess health risks as new tests and options for evaluating them become available. Perhaps unsurprisingly, the experience also enhanced my appreciation for those traditional, unattractive screenings we've trusted for decades: colonoscopies and mammograms.

While no one enjoys doing it, it does provide a benefit that the Gallery test has so far been unable to provide: definitive proof that it saves lives.