The National Cancer Institute made news recently when a group of scientists recommended changing the name of some disease states, no longer calling them “cancers.” Its goal was to address the problem of overdiagnosis.
The ethical ideal of shared decision-making means patients should be able to be involved in medical decisions about their care. These decisions include not just “big ticket” items like surgery, but also supposedly routine measures such as screening tests. To know their choices about screening, patients need to be aware of what overdiagnosis is and how it’s different from false positive results.
Most people understand the basic idea behind a “false positive.” You undergo a screening test and the result is positive for a possible cancer. You then undergo a more definitive, invasive test, such as a biopsy, which is negative. The initial screening test gave you a false answer; there are actually no cancer cells present.
All tests, even the best of them, occasionally give false positive — as well as false negative — results.
For most people, the idea of overdiagnosis is much newer. We used to think that whenever you saw cancer cells under the microscope, you were seeing a disease which, if untreated, would inevitably spread, cause serious problems and eventually kill you. We have recently become aware that cancer is really a wide spectrum of diseases. The spectrum includes what NCI scientists call “indolent” cases.
In indolent disease, the cells look like regular cancer cells but grow very slowly, and never within a person’s lifetime spread widely or cause symptoms. If you never found an early indolent “cancer,” the person would never later on know the difference. In the special case of indolent disease, the mantra we have all been taught, that catching cancer early always leads to better results, simply is not true.
Because we often cannot tell the indolent disease from the truly dangerous cancer, the result may be aggressive treatment for all patients who are diagnosed by screening. Across the population, this means many patients are getting treated, but only a few may actually derive benefit from the treatment.
Therefore, patients who want to make informed choices about whether to have screening tests, and how often to have them, need to understand both the chances of false positive test results and the chances of overdiagnosis.
The NCI scientists obviously want to preserve the great advances we have made by catching and treating the really serious cases of cancer early on, while not causing other patients to suffer from overdiagnosis and overtreatment. Someday, we may have accurate and rapid screening tests that can right away pick out which cases represent indolent disease that we can safely ignore and which cases represent dangerous cancers that we need to jump on immediately.
We’re not there yet, however, which means that informed patients and their physicians may face some difficult choices.