Research News

CT screening in current moderate smokers may be justified as study finds similar lung cancer risk to heavier smokers

BMJ 2015; 351 doi: (Published 20 October 2015) Cite this as: BMJ 2015;351:h5549
  1. Susan Mayor
  1. 1London

Low dose CT (computed tomography) lung cancer screening may be justified in current moderate smokers with a smoking history of 20-29 pack years, says a US study published in the Journal of the National Cancer Institute,1 which found that they had a similar risk of developing lung cancer to heavier smokers and ex-smokers who were currently eligible for screening.

US guidelines recommend low dose CT screening for current and former smokers aged 55-80 with at least 30 pack years of cigarette smoking, and former smokers must have quit within the previous 15 years. One pack year is equivalent to smoking 20 cigarettes (one pack) a day for one year, so 30 pack years equates to smoking 20 cigarettes a day for 30 years or, for example, 40 cigarettes a day for 15 years.

Researchers wanted to know whether people who smoked less heavily, with a smoking history of 20-29 pack years, had a similar risk of lung cancer to heavier smokers. To assess this they analysed data on smokers and ex-smokers from the US Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, which included chest x rays to screen for lung cancer in randomly selected people aged 55-74.

The trial included 18 114 former smokers and 12 243 current heavy smokers (≥30 pack years) who met current US guidelines for low dose CT lung cancer screening, as well as 2283 current moderate smokers (20-29 pack years).

Results showed that the risk of lung cancer was similar in current smokers with a 20-29 pack year smoking history and in current and former smokers with more than 30 pack years after controlling for age and sex (hazard ratio 1.07 (95% confidence interval 0.75 to 1.15)).

“The potential benefits and harms of recommending low dose CT screening for 20-29 pack year current smokers should be assessed,” said the researchers, Paul Pinsky and Barnett Kramer, of the Division of Cancer Prevention at the National Cancer Institute in Bethesda, Maryland, USA. Including this group of more moderate smokers in the low dose CT lung cancer screening programme would increase the number of people eligible for screening by 16.3%, on the basis of self reported smoking data from the US National Health Interview Survey.

Further data from this survey showed a much higher percentage of 20-29 pack year smokers among women than men (22.2% v 12.2%; P<0.001) and among ethnic minorities than non-Hispanic white people (30.0% v 14.1%); P<0.001).

Francine Jacobson, of Brigham and Women’s Hospital in Boston, Massachusetts, wrote in an accompanying editorial that the study’s findings “demonstrate sufficient risk of lung cancer in a population with 20 to 29 pack years to consider screening.”2

Pinsky and Kramer cautioned that the trial on which the current US lung cancer screening recommendations are based did not include smokers with under 30 pack years, so the improved mortality that it showed could not be extrapolated to more moderate smokers. However, they noted that an ongoing Dutch-Belgian study includes people with 20-29 pack years and that the results, expected later this year, will answer this question.


Cite this as: BMJ 2015;351:h5549


  • Clinical Review: Screening for lung cancer using low dose computed tomography (BMJ 2014;348:g2253, doi:10.1136/bmj.g2253)


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