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Lung cancer risk is 10-fold higher in smokers who are not recommended for annual screening

The lung cancer risk of both current light and former heavy smokers for whom screening with a computer tomography (CT) scan is not currently recommended appears to be 10-folder higher than those who have never smoked according to the findings of a study by US researchers.

The World Health Organization estimates that across the globe in 2020, there were 2.21 million cases of lung cancer and which led to 1.8 million deaths. Thus attempts to screen for the early signs of lung cancer might potentially reduce the number of lung cancer deaths.

The development of low-dose helical computed tomography (CT) scanning has shown that low-dose CT enables the detection of many lung cancer tumours at an early stage. In fact, a recent trial concluded that among high-risk individuals who underwent CT screening, lung-cancer mortality was significantly lower compared to those who did not undergo screening.

Consequently, screening recommendations with low-dose computed tomography (LDCT) have been produced and suggest annual screening for adults aged 50 to 80 years who have a 20 pack-year smoking history and currently smoke or have quit within the past 15 years. Screening, however, is not advocated for former smokers with a 20 pack-year or greater smoking history who quit 15 or more years ago (former heavy smokers) or for current smokers with a smoking history of 20 pack-years or less (current non-heavy smokers). The reasons for excluding these two groups is not clear but presumably is related to an expected lower lung cancer risk.

But how valid is this recommended exclusion? This was the basis for the present study in which researchers sought to examine the level of cancer risk among these two groups for whom screening is not recommended.

The researchers used patient data from the Cardiovascular Health Study which enrolled nearly 6,000 community-dwelling older adults (65 years and older) although their analysis was restricted to individuals who were free of cancer at enrolment and for whom pack-year smoking history and smoking cessation data were available. The main outcome of interest was incident lung cancer during follow-up.

Lung cancer risk over time

A total of 4279 participants with a mean age of 72.8 years (57.3% female) were included and followed for a median of 13.3 years. There were 861 current non-heavy smokers and 615 former heavy smokers and 1,973 never smokers who were used as the reference point.

During follow-up, lung cancer occurred in 0.5% of never smokers, 5% of current non-heavy smokers and 5% of former heavy smokers.

The age-adjusted hazard ratio (HR) for incident lung cancer for current non-heavy smokers was 10.06 (95% CI 3.41 – 29.70) and 10.22 (95% CI 4.86 – 21.50) for former heavy smokers, i.e., the two groups for whom screening is not recommended. The mortality risk for current, non-heavy smokers was 53% higher (HR = 1.53, 95% CI 1.22 – 1.92) and 18% higher (HR = 1.18, 95% CI 1.05 – 1.32) for former heavy smokers.

The authors concluded that there appears to be a very high lung cancer risk among those who are excluded from the recommendations for CT screening and called for future studies to examine whether annual screening could reduce lung cancer mortality in these populations.

Faselis C et al. Assessment of Lung Cancer Risk Among Smokers for Whom Annual Screening Is Not Recommended JAMA Oncol 2022