Community-dwelling older adult smokers for whom annual low-dose CT screening is not recommended had a 10-fold higher risk for lung cancer compared with never smokers, according to study results.
The findings, published in JAMA Oncology, indicate a need for prediction models to identify high-risk subsets of older smokers for screening, researchers noted.
Rationale and methods
Annual lung cancer screening with low-dose CT is not recommended for former smokers aged 50 to 80 years who smoked for 20 or more years and who quit 15 or more years ago, or for current smokers with less than 20 pack-years of smoking, according to study background.
Charles Faselis, MD, chief of staff at Veterans Affairs Medical Center and professor of medicine at George Washington University and Uniformed Services University, pooled data from the Cardiovascular Health Study to determine lung cancer risk among 4,279 older smokers (mean age, 72.8 years; 57.3% women; 83.8% white) for whom low-dose CT is not recommended. They categorized study participants as nonheavy smokers if they had fewer than 20 pack-years of smoking (n = 861) and as heavy smokers if they had 20 or more pack-years (n = 1,445).
Researchers assessed incident lung cancer screening during a median 13.3 years (interquartile range, 7.9-18.8) of follow-up. They used a Fine-Gray subdistribution hazard model to estimate incidence of lung cancer in the presence of competing risk for death and Cox cause-specific hazard regression models to estimate HRs and 95% CIs for incident lung cancer.
Among the cohort of nonheavy smokers, the median pack-year smoking history was 7.6 pack-years (IQR, 3.3-13.5) for the 615 former smokers with 15 or more years of smoking cessation, 10 pack-years (IQR, 5.3-14.9) for the 146 former smokers with less than 15 years of smoking cessation and 11.4 pack-years (IQR, 7.3-14.4) for the 100 current smokers.
For those considered heavy smokers, the median pack-year smoking history was 34.8 pack-years (IQR, 26.3-48) among the 516 former smokers with 15 or more years of smoking cessation, 48 pack-years (IQR, 35-70) among the 497 former smokers with less than 15 years of smoking cessation and 48.8 pack-years (IQR, 31.6-57) among the 432 current smokers.
Incident lung cancer diagnoses occurred in10 of 1,973 never smokers (0.5%), five of 100 current smokers (5%) with less than 20 pack-years of smoking, and 26 of 516 former smokers (5%) with 20 or more pack-years of smoking and 15 or more years of smoking cessation.
Moreover, researchers reported cause-specific HRs for incident lung cancer among the two groups not recommended for low-dose CT of 10.54 (95% CI, 3.6-30.83) among current nonheavy smokers and 11.19 (95% CI, 5.4-23.21) among former smokers with less than 15 years of smoking cessation.
After adjusting for age, sex and race, researchers observed HRs compared with never-smokers of 10.06 (95% CI 3.41-29.7) among current nonheavy smokers and 10.22 (95% CI, 4.86-21.5) among former smokers with less than 15 years of smoking cessation.
“A 10-fold or 1,000% higher risk for lung cancer is a substantial risk,” Faselis told Healio. “To put this risk in perspective, participants of the Cardiovascular Health Study with hypertension, which is a major risk factor for heart failure, had a 36% higher risk for heart failure. As smoking is the leading cause of lung cancer, hypertension is a — if not the — leading cause of heart failure. However, only 5% of smokers went on to develop lung cancer.”
Although low-dose CT is superior to chest X-ray in early detection of lung cancer and lowering the risk for lung cancer-associated mortality, it is also associated with a high rate of false-positive results and diagnostic procedures that may result in post-procedure complications, Faselis said.
“Screening all smokers would expose the 95% who do not develop lung cancer to unnecessary physical and emotional harm,” he said. “To a lesser degree, this dilemma also applies to smokers for whom screening is recommended. For example, current heavy smokers have the highest risk for lung cancer — 40 times, or 4,000% — but only 15% of these smokers develop lung cancer. Thus, a collective screening of these smokers will expose the 85% of the same risk for harm.”
Future studies should develop and test risk prediction models, including those based on machine learning or artificial intelligence, to identify smokers who are likely to develop lung cancer so that they can be selected for screening to optimize the risk-benefit ratio of such screening, Faselis added.
“The findings of our study reiterate the importance of abstinence and early smoking cessation for prevention of lung cancer,” he said.
For more information:
Charles Faselis, MD, can be reached at firstname.lastname@example.org.