by Abraham Verghese, MD
I can’t get over the incredible images generated by our latest CT scans and MRI’s. The details of organ anatomy and the 3D reconstructions they can do are just amazing. One side effect of getting such fine resolution, is that more and more we are stumbling onto abnormalities that we were not necessarily looking for–incidentalomas, we call them.
Sometimes the discovery is fortuitous and lifesaving. But often what ensues is worry at the very least, or at the other extreme, painful and expensive tests and procedures which can wind up showing that the incidentaloma could well have been left alone.
Related to this is the problem of over-diagnosis of cancer. We now have tests (prostate-specific antigen, mammograms) that are diagnosing cancers at an early stage, tiny cancers which may or may not have ever come to the patients awareness or caused problems in their lifetime. But having detected the cancer, the wheels are set in motion . . . and what follows is worry, more investigations and treatment such as surgery, radiation and chemotherapy. And the nagging question all through this is: was it necessary?
I heard a wonderful talk here at Stanford last week by Gilbert Welch, M.D. of Dartmouth Medical School, an expert in the field. (He is also the author of “Should I Be Tested for Cancer? Maybe Not and Here’s Why.”) His definition of cancer over-diagnosis is detecting those cancers that grow so slowly that they are destined never to cause a clinical problem, or they actually regress.
But here’s the rub: we can never know which cancer has been ovediagnosed at the time of diagnosis. We can only agree that it was overdiagnosis if the individual is never treated (and turns out to be fine) or dies of something else and the cancer turns out not to be important. Since we can’t know ahead of time, we generally wind up treating everybody.
Dr. Welch felt (and I think many clinicians agree) our threshold for diagnosing cancer is too sensitive.
Here is one example he gave that was very vivid and it has to do with PSA testing for men. Lets say you checked PSAs for 1,000 men between 55 and 70 years of age and you did it annually for ten years. Lets look at the benefits versus harms of such a strategy to ‘find’ prostate cancer “early”.
The benefit: The screening and subsequent treatment will result in your avoiding one cancer death. (Yup, just one, and even that might be generous according to Dr. Welch).
The harm: All those PSA’s will trigger 150-200 false alarms requiring biopsy; it will result in 30-50 over-diagnoses of cancer, and those patients will get unnecessary treatment for prostate cancer (and half of them might have side effects including impotence, incontinence, radiation damage etc). Not to mention worry, worry, worry. Again, the rub is that you can only know if it was over-diagnosis after the fact, if at all.
What Dr. Welch points out is that each of us will look at this benefit/harm equation above and we will decide for ourselves whether this is a “good deal” or “not a good deal.” It’s an individual decision (or should be if we present it well). We would choose what to do depending on how we viewed the world and depending on our attitude to risk.
The solution to over-diagnosis? Dr. Welch suggests that it might be time to raise the threshold for our testing. For PSA for prostate cancer, we might only do a biopsy if there is a nodule on ultrasound rather than blind biopsies for a high PSA; for a mammogram we might consider it abnormal only if the lesion seen is over a centimeter in length. Judging by the mammogram outcry last month, these are going to be tough decisions to make as a society–it is a complex issue.
What was most interesting about Dr. Welch’s presentation was that he did not bring up the economic factors–the money made or saved by these strategies. And I think he was right not to link the discussion to money. These decisions are clinical decisions about difficult and personal choices.
Abraham Verghese is Professor and Senior Associate Chair for the Theory and Practice of Medicine at Stanford University School of Medicine. He is the author of Cutting for Stone and blogs at The Atlantic, where this article was originally published. It is re-posted here with the author’s permission.
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