Medicine Changes

Back in 2008, as a third year medical student, I did a small review of research articles on the topic of CT scans to screen for lung cancer. I've talked about screening extensively in the past, but the idea is to run a test (mammogram, PSA, Pap smear, etc.) on an asymptomatic patient to detect cancer before it causes signs and symptoms. This sounds great until you look at statistics on a population level. If a test is not perfect - that is, if it gives false positives - then it can cause undue burden on that patient, lead to more invasive investigation, and result in adverse outcomes or side effects. Furthermore, even if the test is positive, researchers should prove that catching it earlier benefits patients. This may seem strange, but it's not directly evident that catching a breast cancer a year earlier because of a mammogram done before the lump is felt translates directly into more lives saved.

The problem with lung cancer is that when it becomes symptomatic - coughing blood, difficulty breathing, metastases - it is often too late. This is the kind of disease where screening makes sense. But chest X-rays did not pan out; they aren't sensitive or specific enough - that is, they don't catch many masses and the masses they do catch might not be lung cancer. So CT scans were proposed. When I did the literature search in 2008, I concluded that there was no good evidence that CT scans on asymptomatic smokers would save lives by catching lung cancer earlier. Furthermore, because CT scans are costly, involve radiation, and still have false positives, I concluded that they should not be done for asymptomatic patients.

This is a long-winded introduction to a new guideline I recently read that the American Lung Association now recommends CT scans to screen for cancer in smokers with a 30+ pack year history age 55-74. This fascinates me. In the four years that have lapsed, have our scans become better? Are our radiologists better? Or has there been a new landmark trial? Or are they looking at the data I examined and coming up with a different conclusion?

In the end, this reminds me that medicine changes rapidly. I won't buy the guideline until I examine the literature again - at which time I may be swayed or not. But what we learn, even if it was state-of-the-art up-to-date cutting-edge knowledge a couple years ago, may become old news really quickly. Like technology (the first iPhone was just 5 years ago), the landscape of medicine evolves incredibly rapidly.