A panel of experts commissioned by the US National Cancer Institute says that the word "cancer" may need to be redefined to prevent overdiagnosis and overtreatment of conditions that are often not lethal.
Writing in the July 29 online edition of the Journal of the American Medical Association, the experts say that widespread cancer screening programs turn up too many growths that would not progress to a lethal stage and are considered "indolent".
Most patients do not understand that distinction, however, and "the word 'cancer' often invokes the specter of an inexorably lethal process," wrote Dr Laura Esserman of the University of California, San Francisco, Dr Ian Thompson Jr. of the University of Texas Health Science Center at San Antonio, and Dr Brian Reid of the Fred Hutchinson Cancer Research Institute in Seattle.
Cancer can take "multiple pathways", the three say, "not all of which progress to metastases and death, and include indolent disease that causes no harm during the patient's lifetime."
This re-examination of what constitutes a cancer diagnosis has been spurred by the explosion over the past few decades of sophisticated screening measures such as the mammogram, colonoscopy and the PSA blood test (for prostate cancer). All were heralded as potentially lifesaving, and many predicted that widespread adoption of these tests would catch disease early and cause cancer rates to fall.
But the cancer screening story has turned out differently, the panel noted, because many of the lesions picked up on screening have turned out to be indolent.
"Screening for breast cancer and prostate cancer appears to detect more cancers that are potentially clinically insignificant," the experts said. The same might be said for screens for thyroid cancers and melanomas certainly, lives have been saved because tumours were detected and treated, but "the detection of indolent disease" has risen, too, the panellists wrote.
Issues like this have played out in recent years. The United States Preventive Services Task Force, an influential government panel, caused a furore in 2009 when it called for the abandonment of regular mammography screening for women under 50, reasoning that the benefits of screening for younger women were outweighed by the risks. The same panel also rejected the widespread use of the PSA test, noting that it too often picked up slow-growing lesions that might never harm men's health.
According to the experts writing in JAMA, the best-case scenario for cancer screening is when the tumor is slow-growing but also typically progressive. Colon cancer often acts in this way, the team noted, and colonoscopy has become an "effective" screening program.
In the meantime, however, "overdiagnosis" occurs. The experts say a redefinition of cancer may be needed to quell patient fears over indolent lesions and curb overdiagnosis and overtreatment.
"Use of the term 'cancer' should be reserved for describing lesions with a reasonable likelihood of lethal progression if left untreated," they wrote. Other growths would be classified in a lesser category, "indolent lesions of epithelial origin" (IDLE).
A change in mindset may also be needed for patients and health care workers alike. "Physicians, patents and the general public must recognise that overdiagnosis is common and occurs more frequently with cancer screening," the team wrote.
The recommendations are sure to spur debate, but one outside expert said that debate may be what is needed on this issue.
"We're still having trouble convincing people that the things that get found as a consequence of mammography and PSA testing and other screening devices are not always malignancies in the classical sense that will kill you," Dr Harold Varmus, director of the National Cancer Institute, told The New York Times. "Just as the general public is catching up to this idea, there are scientists who are catching up, too."
But not everyone agrees. Dr Larry Norton is medical director of the Evelyn H. Lauder Breast Center at Memorial Sloan-Kettering Cancer Center in New York City. He said the problem is that even some relatively indolent breast growths, such as ductal carcinoma in situ (DCIS), can go on to become progressive, lethal cancers.
"Which cases of DCIS will turn into an aggressive cancer and which ones won't?" he told the Times. "I wish we knew that. We don't have very accurate ways of looking at tissue and looking at tumours under the microscope and knowing with great certainty that it is a slow-growing cancer."
There's more on cancer detection and diagnosis at the U.S. National Cancer Institute.
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