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Imagine Cancer Testing with a Drop of Blood

The phone call was completely unexpected. A colleague with whom I had trained was in town for the evaluation of a potentially serious problem. She is a highly respected physician from another city, an avid tennis player, and as she headed toward retirement, tennis became a major athletic and social focal point for her life and that of her family.


One crisp fall morning she hurriedly went to the court, did not warm up, did not stretch, and slowly developed a nagging low back pain. The usual interventions of heat, cold, gentle stretching, and a visit with a chiropractor did not help the problem.


She saw a healthcare provider at a free-standing medical clinic who didn’t know the patient’s medical history. Following a very cursory examination, she was whisked off to the on-site MRI scan, and she and her family anxiously awaited the results.


As is often the case, the scan showed myriad abnormalities as completely anticipated for a woman who was 60, and most of these findings were clinically irrelevant and had no bearing on her pain. In other words, there was nothing there.


Nevertheless, the image showed a suspicious area of thickening in one of the vertebral bodies, and the healthcare provider said, “We really do not know what this is, but we should think about doing a biopsy, especially, as you have mentioned, you had that relatively small breast cancer decades ago.”


This kind of finding on a scan (for something else) opens a Pandora’s box of anxiety and uneasiness.


By this time her back problem had improved, of course, but there was that nagging angst about the possibility of something more serious so she elected to come to our medical facility.


A team of specialists weighed in and offered the measured comment that this shadowy finding was nothing, not related to something serious, and by this time her back pain, as expected, had improved using just conservative measures (and time).


In medical terms this is the tyranny of what we call the false positive. This means that an abnormality is detected on a scan, on an X-ray, or in a blood test. The finding when interpreted in the context of the patient’s history and physical examination is an incidental observation and has no significant bearing on the patient’s health or well-being.


Nevertheless, some of these findings need to be followed up now that Pandora’s box has been opened, which can be a source of tremendous anxiety as well as the expense of additional studies and the inconvenience of multiple visits and multiple follow-ups.


The patient has plummeted down the medical rabbit hole. Let me tell you now about another potential rabbit hole—another medical conveyor belt of tests and images and appointments that I mentioned in the headline of this post.


Sophisticated Cancer Detection—Real or Not Yet Ready for Prime Time?


I’m not referring to Theranos, the scam company that claimed to be able to diagnose just about any disease with a drop of blood. Such false promises sent CEO Elizabeth Holmes to prison.


This news is from a leading cancer journal reporting on a national medical trial assessing a blood test that measures circulating cell-free DNA for early detection of cancer. These are highly sophisticated DNA assays that can detect with striking sensitivity the presence of cancer cells in the blood. These trials focus on the potential integration of circulating DNA for the early detection of cancers into a clinical algorithm or workflow. The important words are in boldface.


But now for the challenging part. No test or procedure is 100% foolproof so how do we as empowered patients follow up on an abnormality detected in a blood test that might be insignificant or irrelevant or life-threatening—much like my colleague and her back pain that led to an MRI scan and more testing and worry?


This is where the issue becomes cloudy. It is presently unclear how frequently additional testing should be done if this blood test shows a positive test result. How and where do we search for cancer? With what imaging studies? How frequently are the studies performed and at what point do we stop the testing? And another thorny issue: Who pays for the subsequent investigations?


These programs are not FDA approved nor recommended by professional societies, and some insurance companies will balk at covering these expenses.


If you’ve ever bypassed the gold standard colonoscopy and asked your healthcare provider to order a Cologuard, the at-home colon cancer test instead (where you send off a stool sample by mail), you know that a positive result (blood in the stool) will send you right to the colonoscopy suite anyway, and my physician friends are telling me the Cologuard has a history of false positives (meaning patients are told their test shows blood but the colonoscopy shows no problems). Good news for patients but bad news because they worried for weeks to get in for the colonoscopy.


But this new cancer assay has some promise. In an initial report of 6,290 people who were not known to have cancer, 99.1% received a negative test result. However, among those few with a positive test result, the average time to achieve a resolution that either you have cancer or you do not was 79 days. That can be an agonizing time in dealing with the possibility of a cancer.


Among those few dozen with a positive test, cancer was confirmed in 38% of them (just a few people). That’s also good news for early detection. One researcher in this area commented that, of those with the false-positive test, very few required invasive procedures such as a biopsy or scoping. The big concern is the amount of time (the agonizing wait) to find out what was going on, yes or no. Something or nothing. And how do we move on with our lives with this cloud of uncertainty hanging over us?


Yes, of course, identifying a patient with a serious but early cancer can be life-saving. However, an authoritative review of this topic in a recent issue of the prestigious Annals of Internal Medicine documents that early detection does not necessarily mean a cancer cure.


I am a cancer doctor. Telling a patient they have cancer is difficult. An uncertain cancer screening test is agonizing. Not knowing can be unbearable. I am in favor of the usual screening tests, mammograms, colonoscopies, and until we have more sophisticated tests with better accuracy for some of the cancers that cannot be screened for easily, we should think twice or three times before entering the rabbit hole of diagnosis with an uncertain blood test.


We must recognize the threat of a false positive and the impact that additional studies could have on our lives. For some individuals, their personality and their world view would support going ahead with the sophisticated tests. For other individuals routine screening would be a better fit.


And this opens the door of shared decision-making. The patient and the healthcare provider collaborate to carefully address the pros, the cons, the risks, and the uncertain benefits of the test. And recognize that currently, according to reviewers, there “are no high quality data comparing those who got the test with those who did not (uncertainty due to lack of high quality evidence).”


Be aware, be empowered, understand the potential benefits and also the potential down side from these early studies. The choice is yours.





The PATHFINDER study is reported here: https://ascopost.com/news/september-2022/research-explores-multicancer-early-detection-blood-testing/. The article in the Annals of Internal Medicine is reported here: https://www.acpjournals.org/doi/10.7326/M23-0067.

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