Tuesday, April 12, 2011

Book Review: "Overdiagnosed" and the paradox of cancer survivorship

According to the National Cancer Institute and the Centers for Disease Control and Prevention, the number of cancer survivors in the U.S. has increased dramatically in my lifetime, from 3 million in 1971 to 11.7 million in 2007. From 2001 to 2007 alone, the number of persons living with a cancer diagnosis rose by nearly two million. Most people would probably see these statistics as good news: an indication that our cancer treatments are improving and allowing people to live longer, or that earlier diagnoses are giving people a better chance to survive by catching localized cancers before they spread and become impossible to cure.

Although there is some truth to both of these explanations, they are far from the whole story. As H. Gilbert Welch and colleagues argue convincingly in their new book, Overdiagnosed: Making People Sick in the Pursuit of Health, much of the rise in cancer diagnoses over the past several decades has been the result of overdiagnosis: the detection (through screening or incidental finding on medical images obtained for other reasons) of cancers that would otherwise never have caused problems for patients. In the absence of screening, patients would not have developed symptoms because the "cancer" would not have progressed, or the patient was destined to die from some other cause (typically, heart disease). In the presence of screening, however, they suffer the psychological effects of knowing that they have cancer, the complications of diagnostic procedures, and the consequences of unnecessary treatments.

Seen in this light, the rise in cancer survivorship is not a modern medical success story. For millions of patients who received diagnoses that they didn't need and would do nothing to improve their health, it is a catastrophe.

Consider the example of prostate cancer. In a 2009 analysis published in the Journal of the National Cancer Institute, Dr. Welch and prostate cancer expert Dr. Peter Albertsen used data from the NCI's Surveillance, Epidemiology, and End Results (SEER) program to estimate that the introduction of prostate-specific antigen (PSA) screening in 1986 led to an additional 1.3 million U.S. men receiving a prostate cancer diagnosis through 2005. More than 1 million of those men were treated with surgery, radiation, or both. If one assumes optimistically that the entire decline in prostate cancer deaths during this time period can be credited to earlier detection of curable prostate cancers, then 22 out of 23 men who were diagnosed, and 17 out of 18 men who were treated, received no health benefit from their cancer diagnosis. (And that's an optimistic estimate; a 2009 European study put the figure at 47 out of 48.)

When we look harder for asymptomatic cancers and other "silent" diseases such as diabetes and osteoporosis, Dr. Welch argues, we occasionally catch them at more curable stages, but far more commonly find diseases years earlier than we needed to, or that we didn't need to find in the first place. I recall the timeless advice passed on by one of my attending physicians in residency regarding the dangers of heroic interventions: "Don't just do something, stand there!" But doctors (myself included) have a very hard time doing nothing in a patient with a cancer diagnosis, even if patients weren't already conditioned by the popular "War on Cancer" to want to eradicate every abnormal cell from their bodies, regardless of the risks.

I recommend Overdiagnosed to all health professionals and patients as a highly readable cautionary tale of the excessive diagnostic capacity inherent in modern medicine. Screening for selected diseases has its place, of course, but overenthusiastic and uninformed screening in the pursuit of health is more likely to do harm than good, by making people sick for no reason. And stripping away a person's sense of wellness is no small thing, as Dr. Clifton Meador wrote in his 1994 essay "The Last Well Person":

The demands of the public for definitive wellness are colliding with the public's belief in a diagnostic system that can find only disease. A public in dogged pursuit of the unobtainable, combined with clinicians whose tools are powerful enough to find very small lesions, is a setup for diagnostic excess. And false positives are the arithmetically certain result of applying a disease-defining system to a population that is mostly well. ... If the behavior of doctors and the public continues unabated, eventually every well person will be labeled sick. Like the invalids, we will all be assigned to one diagnosis-related group or another. How long will it take to find every single lesion in every person? Who will be the last well person?