The recommendation applies to current smokers and those who have quit within the past 15 years who have at least a 30-pack-year history of smoking, defined as smoking one pack a day for 30 years or two packs a day for 15 years. For all other adults, the task force does not recommend routine screening for lung cancer using low-dose CT.
The task force concluded there is no benefit of CT screening in adults younger than 55 and older than 74, or in those regarded as having a lower risk for lung cancer, such as adults who have less than a 30-pack-year smoking history or those who stopped smoking more than 15 years ago (CMAJ, March 7, 2016).
The guidelines differ from the task force's recommendation in 2003, which called for no screening of asymptomatic adults for lung cancer with chest radiography and insufficient evidence to support screening using low-dose CT in asymptomatic adults. In this current recommendation, the task force does not recommend the use of chest x-ray, with or without cytology, to screen for lung cancer.
The task force cited results from the National Lung Screening Trial (NLST) in the U.S., which found a 20% mortality benefit to using low-dose CT to screen high-risk individuals.
The recommendation does not apply to adults with previous lung cancer or signs or symptoms of lung cancer. The task force noted that 322 people would have to be screened with low-dose CT to prevent one death due to lung cancer over 6.5 years.
The task force wrote that it is "taking a more conservative approach" because it calls for three annual consecutive scans rather than continuous annual or biennial scans. There is "limited evidence for the optimal duration and interval for lung cancer screening," suggesting there is not a basis of evidence to support ongoing screening after three initial yearly scans and interval screening, such as annual or biennial, the authors added.
The guidelines are also more conservative than those adopted in the U.S. by recommending that screening stop at age 74, rather than 80.
The Canadian task force members noted that mortality in late-stage lung cancer is much lower than in earlier stages: Data from the American Cancer Society showed five-year survival rates for stage IV and IA lung cancer of 1% and 49%, respectively, in 2007.
In Canadian Cancer Statistics 2015, released by the Canadian Cancer Society, it was estimated that 26,000 Canadians would be diagnosed with lung cancer. More Canadians die from lung cancer than breast cancer, colorectal cancer, and prostate cancer combined.
The Canadian Association of Radiologists (CAR) did not provide a comment on the task force's new guideline. For its part, CAR is developing its own guidelines on CT lung cancer screening that are scheduled to be released this summer.
"Most lung cancers are not symptomatic until they have advanced to late stages of the disease and are incurable," said Dr. Natasha Leighl, president of Lung Cancer Canada, in a statement. "That's why it's encouraging to see these guidelines, which recommend a screening test that could lower mortality -- representing a chance to save lives."
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