Screening for the early detection of cancer saves lives. You’d have to look hard to find a medical professional who disagrees with that statement. But you can find some.
The American Cancer Society has specific recommendations about screening for breast, cervical, lung, and colon cancer. So do the CDC and Mayo Clinic.
“We recommend cervical cancer screening start at age 21, and continue thereafter about every three to five years, depending on the type of screening that’s performed,” said Dr. Kristina Butler, an OB-GYN at the Mayo Clinic. Mayo also has recommendations for regular screenings for colon and breast cancer and suggests consulting with your doctors for other possible cancer screenings.
Dr. Gilbert Welch is not so sure. He says that massive screening for cancer has the potential to find abnormalities that are not life-threatening, which overestimates the true survival rate of certain cancers and falsely inflates the number of cancer survivors. He calls this "cancer over-diagnosis."
“A cancer diagnosis regularly leads to cancer treatment, and an overdiagnosed patient cannot be helped by treatment, because there’s nothing to fix,” said Welch. “But they can be harmed. And we doctors don’t want to be in the business of harming patients.”
Welch is a cancer epidemiologist and senior researcher at the Center for Surgery and Public Health at Brigham & Women’s Hospital in Boston. For more than three decades, he has been asking hard questions about his profession. His arguments are frequently considered counterintuitive, even heretical by the medical community. He is the lead author of a review article in the January issue of the journal Clinical Chemistry titled “Cancer Screening, Incidental Detection, and Overdiagnosis."
“In the past, patients were only diagnosed with cancer because they had symptoms," explained Welch. "Now we evaluate looking for cancers in individuals who have no signs or symptoms of cancer. That’s screening."
“In addition, patients who have symptoms from illness or injuries that have nothing to do with cancer are being more intensively tested. Particularly with advanced imaging, things like CT, MRI, PET scan, leading us to stumble onto some cancers. That’s incidental detection. In short, screening is purposeful; incidental detection is unintended. But they both lead to the same result, the diagnosis of cancer in patients who have no symptoms of the disease.”
That’s what Welch calls cancer overdiagnosis — finding abnormalities that are technically cancers but will never cause symptoms or death and would be better left alone.
Of course, there are cancers where treatment is needed and those treatments can be much more effective if the cancers are detected early. To illustrate the differences, Welch describes what he calls the “barnyard example” of the birds, the rabbits and the turtles.
“The goal of screening is to fence them in, you know, to catch them early,” he said. "However, you see the problem with the birds. We can’t catch the birds because they’ve already flown away. Birds represent the most aggressive cancers, the fastest growing cancers, the cancers that have already spread by the time they are detectable. Screening doesn’t help with the birds. The question is, ‘Can we treat them?’
“Now, the rabbits are hopping around and you can catch them early if you build enough fences. So screening may help in these cases.
“And then there are the turtles. And here we don’t need any fences, because they are not going anywhere anyway. Turtles meet the pathologic definition of cancer, however, they are either not growing or growing so slowly that they will never cause problems until the patient dies from other causes.”
Welch admits he is an outlier in the medical community and says there is no one right answer for everyone. He says that he got his colonoscopy at age 50 but does not have his prostate-specific antigen (PSA) checked for prostate cancer. He says everyone should discuss these personal medical decisions with their health care providers.
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