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Overdiagnosis occurs when tumours are detected that if left untreated would not cause harm during the patient's lifetime. (Eric Gaillard/Reuters)

The definition of cancer should be narrowed to exclude some forms of the disease that are unlikely to cause harm, U.S. cancer experts propose.

That's one of the recommendations from a working group of the U.S. National Cancer Institute, which published an online commentary today in the Journal of the American Medical Association.

"The word 'cancer' often invokes the specter of an inexorably lethal process," said Dr. Laura Esserman, director of the Carol Franc Buck Breast Care Center at the University of California in San Francisco, along with her co-authors.

"Use of the term 'cancer' should be reserved for describing lesions with a reasonable likelihood of lethal progression if left untreated."

Esserman and her co-authors gave the example of a premalignant condition currently called ductal carcinoma in situ. Detecting and removing such lesions has not led to lower incidence of invasive cancer, the U.S. doctors said.

The authors say doctors, patients and the general public need to recognize that overdiagnosis is common and occurs more frequently with cancer screening. Overdiagnosis occurs after the detection of tumours which, if left untreated, would not cause harm during the patient's lifetime.

Identifying "indolent" cancers that cause no harm during the patient's lifetime is common in breast, lung, prostate and thyroid cancer, the authors said.

The frequency of screening depends on the cancer’s growth rate. For indolent tumours, detection is potentially harmful because it can result in overtreatment.

Conversely, screening is ideal for slow-growing but progressive forms with a precancerous lesion, such as polyps for colon cancer or lesions for cervical cancer.

The authors' suggestions also include:

  • Bringing experts in pathology, surgery and imaging together with advocates "to revise the taxonomy of lesions now called cancer."
  • Creating "observational registries" to generate data on tumour growth rates over time so patients with conditions that are unlikely to become cancer can confidently select less invasive treatments.
  • Mitigating overdiagnosis, such as by focusing screening on high-risk populations and reducing frequency of screening exams.

"Although no physician has the intention to overtreat or overdiagnose cancer, screening and patient awareness have increased the chance of identifying a spectrum of cancers, some of which are not life-threatening."

The recommendations were based on a meeting last March convened by the U.S. National Cancer Institute to evaluate the problem of overdiagnosis.