What characteristics define your most ideal screening test?
Answers from an internist and an oncologist
I recently had the privilege of interviewing Chadi Nabhan about his new book, The Cancer Journey, for The Clinical Excellence Podcast. Chadi and I have known each other for years and it is always a pleasure to catch up. The Cancer Journey is an excellent book that I think is useful not only to patients and their families but to anyone in a “medicine-adjacent” field. The book includes a very readable and intelligent chapter about cancer screening. We didn’t talk about screening on the podcast, maybe because he and I part ways on the topic, Chadi more on the enthusiast side of the spectrum and me more on the skeptic side.
After we recorded, Chadi sent me a note asking the question, "What characteristics define your most ideal screening test?" I liked the question and asked Chadi if he wanted to co-author one of our Sensible Medicine “debate” posts: one question, two or more authors, 500 words or less, the authors don’t see each other’s posts before publication. He graciously agreed.
Adam Cifu
First, Dr. Chadi Nabhan
Going up against Adam Cifu is no easy feat. I admire the thoughtful physician in Adam and have had the privilege of working alongside him during my time at The University of Chicago. I witnessed firsthand his humanistic nature and his astute, critical appraisal of medical literature. He also has a Substack—while I don’t. So, clearly, he must know more than I do. But does he?
Did I have a PSA to screen for prostate cancer? I have.
Did Adam have a PSA for the same reason? I bet.
Did I have a colonoscopy to screen for colon cancer at some point? Yes. I suspect Adam, also.
So, why is Adam all up in arms about screening tests if he subjects himself to the same? You’ll need to ask him, but our posts may clarify his opinion and where we diverge.
After two decades in medicine and oncology, I’ve learned to accept the imperfections inherent to our field, which is why I am comfortable with screening.
See, science isn’t perfect – nothing is (well, except the books I’ve written). We can’t always have the perfect study, endpoints, inclusion/exclusion criteria, or perfect everything. Despite these imperfections, we’ve learned to guide patients through the many uncertainties that medicine often presents.
Voltaire once said, “Don’t make perfect the enemy of good.” I try to live by this and suggest you do as well. Seems like Voltaire and I have something in common.
So, I’ll come out and admit immediately: there is no perfect screening test or even a perfect clinical trial. In fact, I am asking Adam to design the perfect screening trial with the end point he trusts, the enrollees he proposes, and for a disease of his choosing, and I promise that I can poke holes in that study, because no study is perfect.
However, screening tests deserve closer scrutiny, as they target healthy individuals to detect cancers at a curable stage—a noble, but challenging goal
There are false positives when we end up performing expensive tests on benign findings, some of which carry complications. We may detect cancers that will never pose a threat or don’t require immediate intervention. Also, a negative test may miss an existing cancer, giving a false sense of security. False positives and negatives are an inherent part of screening. Can you find me a screening test that is 100% sensitive AND 100% specific? Don’t bother—such a test doesn’t exist.
Of course, we all want a screening test to reduce our risk of dying, but perhaps reducing the risk of dying from the specific cancer the test is destined to detect is “good enough”? Critics argue that the procedures to follow an abnormal finding are risky, even fatal. I believe these risks are often exaggerated—every medical intervention carries risk, from Tylenol to Adam’s yearly flu shot.
Despite the imperfections and limitations of screening tests (listing all screening studies across all cancers and scrutinizing them is beyond the scope of this opinion piece) I believe that screening select people who meet high risk criteria is a valuable and acceptable practice. By engaging in shared decision making, we can effectively balance the trade-offs involved in testing.
Let’s have a conversation about the pros and cons so that each person can make a decision that is most suitable to their individual situation. I plan on having that conversation with Adam regarding his future colonoscopy.
Second, Dr. Adam Cifu
I’ve probably already written too much about screening on this site. But, as I noted above, I really liked the way this question organized my thinking in a new way.
My first idea for this column was to go back to the traditional “characteristics of successful screening tests” slide and explain each of the points.
Then I realized this would be a cop-out. Not only have I already done this, but I have to admit that none of our screening tests, including those I discuss with my patients daily, fulfill these criteria. There is no cheap and widely acceptable test that screens for a common, serious disease in the preclinical stage. There is no test that has perfect test characteristics, reliably ruling out dangerous diseases while diagnosing only cancers that warrant treatment. There is no screening test that, when applied to an average risk population, decreases all-cause mortality.1
Because no screening test fulfills these five criteria, I realized that this slide is missing a bullet point.
Reliable data on all potential effects (positive and negative) of screening must be easily available.
We don’t really have this for our screening tests, though efforts have been made to abstract it from the data we do have. This is my favorite right now.
So, the characteristics that define my most ideal screening test are the five above, with the additional new bullet point. This would allow me to actually have intelligent conversations with my patients. Using the data from the link above, the conversation would sound something like this:
If you get this test, you will be 2.9% more likely to be diagnosed with prostate cancer, about a 12% chance over 15 years.
You will be 0.17% less likely to die of prostate cancer (but you will be at risk of the side effects of treatment -- incontinence, ED, financial harm). Your chance of dying of prostate cancer if you get screened is 0.71% vs. 0.88% without screening.
If you get screened, you will be 3.1% more likely to be diagnosed with prostate cancer that would not have caused you any harm (this is what we call overdiagnosis). If you are part of this group (6.5% with screening compared with 3.4% without), anything you do about your diagnosis only has the potential to do harm (incontinence, ED, financial harm).
This is not simple, but most medical decisions are not. Give me reliable data like this before we approve and pay for screening tests. Then, although I won’t be able to tell you what my ideal screening test is, my patients will only agree to screening tests that are ideal for them.
Pap smears for cervical cancer screening and prevention probably come the closest to this ideal test though I am in no position to say it is an acceptable test. Also, its importance on a population level, as HPV vaccination becomes more prevalent, is falling.
Photo Credit: Hush Naidoo Jade
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The flaw in Dr Nabhan’s argument surfaced when he wrote “ I believe that screening select people who meet high risk criteria is a valuable and acceptable practice” the problem with that statement is that screening is aimed at an entire population not just a select few who meet high risk criteria. For example, take mammograms. All women are encouraged, dare I say required through subtle and not so subtle pressure to undergo a painful and not at all benign procedure beginning early in their lives and continuing yearly for the entirety of it. There is data to support that mammograms do not decrease overall mortality. Many lesions are found that had they been ignored would have led to a far better quality of life. I think of the Medical model similar to the Titanic with everyone grasping to hold onto it and salvage what they can. Yes it may help some, but it also injures many. I’ve heard Dr. Prasad comment on this many times. Innovations are slow to turn that ship around because there is so much money invested in the status quo. For example, there are new alternatives to ionizing radiation mammograms that are not offered to women or covered by insurance. There are new procedures for dealing with early stage breast cancer that also are not offered to women or covered by insurance.
I doubt that I will see a change in my lifetime, but Hope springs eternal.
Nearing age 75 and no more screening tests for me other than an occasional blood test perhaps. This assumes that getting screened and finding some bad thing further assumes that the medical mafia has the cure. 95% of the time, it does not.
I will eventually die from something and there is no way any medical expert can say that they could have done something to keep me ticking. That sentiment, like most medicine, is purely guesswork or perhaps you fall somewhere on a chart showing probabilities of living or dying.
The individual never fits the probabilities of the masses. We are not to be treated as a one-size-fits-all number as medicine so easily does.