Lung cancer risk model refines decisions to screen

Computed Tomography (CT) screening can identify lung tumors while they are still treatable, and the US National Lung Screening Trial (NLST) found that annual screening of high-risk smokers can reduce lung cancer mortality by 20%. The best way to identify those at high risk remains an important question. The U.S. Preventive Services Task Force (USPSTF) recommends annual screening based on hard cutoffs for age and smoking duration/intensity, and doesn't recommend screening former smokers who quit more than 15 years ago. The PLCOm2012 model was developed based on studying lung cancer incidence in participants from the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial (PLCO). In addition to considering age, smoking duration/intensity, and quit time of former smokers, PLCOm2012 also considers race/ethnicity, socioeconomic circumstance, body mass index, personal history of cancer, chronic obstructive pulmonary disease, and family history of lung cancer to determine a risk score for lung cancer.

Tammemägi and colleagues used data from the NLST to identify a risk threshold (PLCOm2012 score ≥ 0.0151) to identify people who should receive annual CT screening. This threshold was applied, alongside the USPSTF criteria, to smokers who were screened in the PLCO trial. The authors found that 8.8% fewer people exceeded the threshold than met the USPSTF criteria (p < 0.001), but 12.4% more lung cancers were identified using the threshold. Using the threshold resulted in higher sensitivity (80.1% [95% CI 76.8%-83.0%] versus 71.2% [95% CI 67.6%-74.6%], p < 0.001), specificity (66.2% [95% CI 65.7%-66.7%] versus 62.7% [95% CI 62.2%-63.1%], p < 0.001), and positive predictive values (4.2% [95% CI 3.9%-4.6%] versus 3.4% [95% CI 3.1%-3.7%], p < 0.001) than UPSTF criteria. The authors noted that 8.5% of smokers who quit more than 15 years ago exceeded the PLCOm2012 threshold, and there were no never-smokers who exceeded the threshold. Additionally, risks and incidence of lung cancer were significantly greater for smokers aged ≥65-80 years than among those aged 55-64 years.

Applying the PLCOm2012 risk threshold can more efficiently identify candidates for CT screening than the USPSTF criteria.

The authors say: "This should make lung cancer screening more attractive for policy-makers, and more affordable for health systems."