There are few topics in medicine more controversial than screening. This is for a number of reasons. The first is that early detection or screening has an intuitive logic to it for both laymen and physicians that is irresistible and that argues for the commonsense use of putative screening tests, even in the absence of evidence supporting their use. If a test can theoretically pick up a cancer early and if cancers diagnosed early do better than cancers diagnosed late, then common sense dictates that it must be good to utilize the test. And even if it is not great, what the heck—it cannot be harmful!
The reality is that this syllogism in most instances simply does not prove to be true—early detection does not prove to be beneficial in most instances, even if logic says it must; and furthermore, yes, screening tests can be harmful. The tests themselves or the follow-up tests can have complications; they have financial costs (even if the insurance company is paying for the test); a negative test may give a false sense of security; and the biggest problem is the large number of false positives that accompany most screening tests and that require further evaluation. For tests that are highly efficacious and beneficial, like colonoscopy, the risk-benefit ratio is very worthwhile, but I point these issues out simply to indicate that screening tests are not risk-free, just like anything else in medicine.
Another reason screening is controversial is that most people, including professionals, don’t understand or appreciate the true purpose of screening—it is not to find or diagnose cancer. The purpose of screening is to reduce mortality from cancer. Obviously, we have to find and diagnose cancer on the way to reducing mortality. However, many potential tests can find or diagnose cancers for which we can do little or we can help patients equally well whether the cancer is detected/diagnosed earlier or later. But the real point is whether we can actually save lives that otherwise would not have been saved. As a second condition for a test to be recommended, it must also be cost-effective—we don’t recommend tests that cost thousands of dollars on a monthly basis even if that might save some lives—it would simply not be feasible.
Many tests have been utilized by clinicians in the absence of evidence that support their use; and subsequently randomized trials have shown that these tests were ineffective. I would certainly advocate that my readers undertake screening that is proven to be advantageous and worthwhile, such as breast, cervical and colorectal screening. In this and my next two articles, to illustrate the principles of screening, rather than discussing screening tests that are recommended for use, we will review some of the tests that have been rejected.
Perhaps the most logical screening test in the past was the simple chest X-ray. It is cheap, easily available and can be used to detect a highly fatal cancer. Surgery can cure lung cancer that is diagnosed early and hence there is a logic to attempt to catch these tumors earlier when the outcome with surgery is better.
In the past, I dare say many primary care physicians made the chest X-ray a routine part of the annual wellness exam for middle- and older-age patients with a history of smoking who were at significant risk of lung cancer. This was logical and well intentioned. Over the years, there were three randomized trials that were done and published, all quite large and well conducted, that each demonstrated quite conclusively that the chest X-ray had no benefit in reducing mortality from lung cancer. These trials may have slowed its use but certainly did not halt it. Furthermore, there were some improvements in the X-ray machine itself that made it more sensitive and therefore kept up enthusiasm for its use.
Finally, a fourth large trial was conducted to evaluate the efficacy of chest X-ray screening. Its results were published in the Journal of the American Medical Association in 2011. There were 77,445 people randomized to annual chest X-rays for four years versus 77,456 people who were in the control group. Both groups were followed for 13 years. At the end of that time, there were 1,213 lung cancer deaths in the experimental arm versus 1,230 lung cancer deaths in the control arm, obviously no difference.
Subsequently studies have shown that screening with low-dose chest CT scans can indeed reduce lung cancer mortality, whereas plain chest X-rays cannot. Why? CT scans can detect dramatically smaller lesions than chest X-rays and perhaps that is what makes the difference.
The real point, though, is that one cannot rely on intuition and logic in making clinical decisions, particularly in the area of screening. We cannot do a randomized trial for every circumstance in medicine, but when we can, we need to heed the results. Parenthetically, low-dose chest CT scans are now recommended for screening for lung cancer for current or past heavy smokers, as they reduce mortality by about 20%.
Alfred I. Neugut, MD, PhD, is a medical oncologist and cancer epidemiologist at Columbia University Irving Medical Center/New York Presbyterian and Mailman School of Public Health in New York.
This article is for educational purposes only and is not intended to be a substitute for professional medical advice, diagnosis, or treatment, and does not constitute medical or other professional advice. Always seek the advice of your qualified health provider with any questions you may have regarding a medical condition or treatment.