Smoking Reduction, Cessation Lowers Lung Cancer Risk in Patients With COPD

Smoking reduction and cessation lowered the risk of lung cancer in patients with chronic obstructive pulmonary disease (COPD) who smoked less than 30 pack-years in a study published in Respiratory Research.

The researchers explained that comorbidities are common in patients with COPD, with lung cancer being one of the most frequent and burdensome; it is the leading cause of death in patients with COPD. Cigarette smoking is a common risk factor for both lung cancer and COPD, and it further increases the risk of lung cancer in patients with COPD. They explained that patients with COPD must attain complete smoking cessation to reduce lung cancer risk.

Few past studies have investigated the effect of smoking habit changes on lung cancer-related outcomes in patients with COPD. Consequently, the researchers conducted a nationwide cohort study to evaluate the impact of smoking reduction on lung cancer diagnosis after a COPD diagnosis in smokers using less than 30 pack-years.

Man refusing cigarettes | Image Credit: vchalup - stock.adobe.com

To do so, the researchers used data from the Korean National Health Insurance System (K-NHIS) database, which contains information on South Korean patient demographics, medical treatments, procedures, diagnostic codes, prescription drugs, and hospital use. The K-NHIS database also includes data from the National Health Screening Examination, a standardized health screening program provided to all insured persons every 2 years; it involves a self-administered questionnaire on medical history, lifestyle habits, anthropometric measurements, and laboratory tests.

The database included all patients 40 years or older with COPD between January 1, 2014, and December 31, 2019. COPD was defined as the presence of a J43 through J44 code and the prescription of COPD medication, like long-acting muscarinic antagonists (LAMAs), long-acting beta-2 agonists (LABAs), or inhaled corticosteroids (ICS), at least twice within 1 year.

Also, smoking status was assessed using a self-reported questionnaire within 2 years before COPD diagnosis (Exam 1) and within 3 years after COPD diagnosis (Exam 2). Current smokers were questioned about their duration of smoking and the mean number of cigarettes smoked per day. The researchers used these data to define the patients as light (<10 cigarettes per day), moderate (10-19 cigarettes per day), or heavy smokers (≥20 cigarettes per day).

Of the eligible patients with COPD in the database, the researchers only considered the 45,271 who began smoking before their COPD diagnosis. After narrowing it down, the study population consisted of 16,832 participants who had smoked less than 30 pack-years. Based on Exam 1, they considered 3778 (22.4%) to be light smokers, 9477 (56.3%) to be moderate smokers, and 3577 (21.3%) to be heavy smokers. Additionally, the study population consisted of mostly men (87.3%), and the median age was 64 years.

Changes in cigarette smoking intensity from Exam 1 to Exam 2 were determined based on relative fluctuations in the number of cigarettes smoked per day. The researchers categorized the patients into 3 groups based on these changes: quitters (those who completely stopped smoking), reducers (those who decreased their number of cigarettes consumed per day by 20% or more), or sustainers (those who increased or decreased the number of cigarettes consumed per day by less than 20%).

Of the study population, 7859 (46.7%) continued smoking, 2323 (16.8%) reduced smoking, and 6150 (36.5%) quit smoking after their respective COPD diagnoses. Of the reducers, 1498 and 1325 reduced daily smoking amounts by between 20% to 50% and more than 50%, respectively. Compared with sustainers, reducers and quitters were more likely to be older, have more comorbidities, and have a severe exacerbation history.

During a median follow-up of 3.94 years, there were 469 new lung cancer diagnoses among the study population. The researchers explained that reducers (adjusted HR [aHR], 0.74; 95% CI, 0.56-0.98) and quitters (aHR, 0.78; 95% CI, 0.64-0.96) had a significantly lower risk of lung cancer than sustainers. Consequently, the incidence of lung cancer showed a decreasing trend with a decreasing amount of smoking (P for linearity < .01).

The researchers acknowledged their study’s limitations, one being that spirometric measurements are not available in K-NHIS data; this meant that COPD diagnosis was based on administrative data, which may have resulted in misclassification bias. Also, smoking habits were self-reported through questionnaires rather than confirmed through biochemical methods, which may lead to recall, misclassification, and measurement errors. Despite these limitations, the researchers emphasized the importance of smoking cessation, especially in patients with COPD.

“Reducing the smoking amount might be a starting point for individuals who struggle to quit abruptly with active encouragement of smoking cessation in every clinic, as smoking cessation is the single most effective way not only to reduce lung cancer development and mortality in patients with COPD, but also to ameliorate the natural course of COPD,” the authors concluded.

Reference

Shin SH, Kim T, Kim H, Cho J, Kang D, Park HY. Impact of smoking reduction on lung cancer risk in patients with COPD who smoked fewer than 30 pack-years: a nationwide population-based cohort study. Respir Res. 2024;25(1):133. doi:10.1186/s12931-024-02741-1