“Early detection of cancer saves lives.”
How many times have you heard this statement or something resembling it? It’s a common assumption (indeed, a seemingly common sense assumption) that detecting cancer early is always a good thing. Why wouldn’t it always be a good thing, after all? For many cancers, such as breast cancer and colon cancer, there’s little doubt tha early detection at the very least makes the job of treating the cancer easier. Also, the cancer is detected at an earlier stage almost by definition. But does earlier detection save lives? This question, as you might expect, depends upon the tumor, its biology, and the quality and cost of the screening modality used to detect the cancer. Indeed, it turns out that the question of whether early detection saves lives is a much more complicated question to answer than you probably think, a question that even many doctors have trouble with. It’s also a question that can be argued too far in the other direction. In other words, in the same way that boosters of early detection of various cancers may sometimes oversell the benefits of early detection, there is a contingent that takes a somewhat nihilistic view of the value of screening and argues that it doesn’t save lives.
A corrollary of the latter point is that some boosters of so-called “alternative” medicine take the complexity of evaluating the effect of early screening on cancer mortality and the known trend towards diagnosing earlier and earlier stage tumors as saying that our treatments for cancer are mostly worthless and that the only reason we are apparently doing better against cancer is because of early diagnosis of lesions that would never progress. Here is a typical such comment from a frequent commenter whose hyperbolic style will likely be immediately recognizable to regular readers here:
Most cancer goes away, or never progresses, even with NO medical treatment. Most people who get cancer never know it. At least in the past, before early diagnosis they never knew it.
Now many people are diagnosed and treated, and they never get sick or die from cancer. But this would have also been the case if they were never diagnosed or treated.
Maybe early diagnosis and treatment do save the lives of a small percentage of all who are treated. Maybe not. We don’t know.
As is so often the case with such simplistic black and white statements, there is a grain of truth buried under the absolutist statement but it’s buried so deep that it’s well-nigh unrecognizable. Because we see this sort of statement frequently, I thought it would be worthwhile to discuss some of the issues that make the reduction of mortality from cancer so difficult to achieve through screening. I will do this in two parts, although the next part may not necessarily appear next week