The potential risks and harms of low-dose CT (LDCT) lung cancer screening in current 20- to 29-pack–year smokers needs to be assessed before recommending LDCT for this group, according to a study published in the JNCI: Journal of the National Cancer Institute (2015; doi:10.1093/jnci/djv226).

Recently, recommendations made by the US Preventive Services Task Force (USPSTF) stated that eligibility criteria for LDCT lung cancer screening includes a cigarette smoking history of 30+ pack-years and, if a former smoker, having quit smoking within the last 15 years in patients age 55 to 80 years. 

The USPSTF recommendations matched the eligibility criteria of the National Lung Screening Trial (NLST), except that the upper age limit for entering the NLST was 74 years. Guidelines from the National Comprehensive Cancer Network (NCCN), however, recommend screening for persons with NLST-defined smoking history criteria but also suggests those with a 20+ pack-year smoking history and one additional lung cancer risk factor (such as occupational exposure or pulmonary disease history) could also be eligible for screening. 

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Although many studies have shown the risk for lung cancer is much lower in persons who have quit smoking, the risk for those who have smoked 20 to 29 pack-years remains unknown.

To determine the risk of lung cancer in those who smoked 20 to 29 pack-years, Paul F. Pinsky, PhD, and Barnett S. Kramer, PhD, both of the National Cancer Institute in Bethesda, Maryland, looked at data from the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial (PLCO).

PLCO was a randomly assigned screening trial of participants age 55 to 74 years with chest radiographs (CXR) used for lung cancer. Participants completed a baseline questionnaire that asked questions regarding smoking history. The researchers also used data from the National Health Interview Survey (NHIS), which looked at the smoking history and race/ethnicity of subjects and the demographic profiles of various high-risk smoking history categories. Models were adjusted to account for age and sex of the participants.

The researchers found that the risk of lung cancer among 20- to 29-pack–year current smokers was similar to that of 30+ pack-year former smokers who meet the current guidelines for LDCT set by the USPSTF. Further, based on the NHIS data, current 20 to 29 pack-year smokers were more likely to be female and to be racial/ethnic minorities than were those meeting the current USPSTF guidelines.

Despite this, the researchers feel that the guidelines should be approached cautiously in terms of recommending screening to 20- to 29-pack–year current smokers. 

“This group was not included in the NLST, so there is the untested assumption that the trial’s mortality benefit can be extrapolated to them,” the researchers wrote.  “Until LDCT screening performance in population settings is better understood, expansion of screening to additional populations may incur unanticipated harms.”

In an accompanying editorial (doi:10.1093/jnci/djv286), Francine L. Jacobson, MD, MPH, of Brigham and Women’s Hospital in Boston, Massachusetts, wrote that the findings in the accompanying study “demonstrate sufficient risk of lung cancer in a population with 20 to 29 pack-years to consider screening … As we eliminate arbitrary divisions instituted for managing clinical trials, we can approach important questions about differences in risk.”