The incidental discovery of pulmonary nodules on imaging studies of the chest or through dedicated screening programs for the detection of lung cancer is common. It is estimated that 1.57 million nodules are detected incidentally every year, 5% of which are malignant.¹ The incidence of pulmonary nodules in lung cancer screening programs has been reported at approximately 27%, with 1.1% of patients diagnosed with lung cancer.² Guidelines have been published to aid physicians in managing these nodules.^3–5 Examples of benign causes of pulmonary nodules are listed in Table 1.⁶ All patients with a pulmonary nodule and a history of malignancy, with multiple nodules but no dominant nodule, with any pulmonary mass (i.e., lung opacity of greater than 3 cm in diameter), or who are immunocompromised should be referred to a pulmonologist for further workup.⁷

What Nodule and Patient Characteristics Suggest a Malignant Cause?

The risk of malignancy is higher in solid nodules that are large, have irregular borders, have asymmetric calcifications, have a volume doubling time between one month and one year, or are in the upper lung lobes. Subsolid nodules are more likely to be cancerous than solid nodules. Increasing age and history of cigarette smoking are associated with a higher risk of lung cancer.

EVIDENCE SUMMARY

Malignancy is more common in solid nodules that are 6 mm or greater in diameter.³ Other nodule characteristics associated with cancer include location in the upper lung lobes, irregular or spiculated borders, ground-glass appearance, or punctate or eccentric calcifications⁷ (Figure 1⁸). Nodules with a volume doubling time of more than 30 days to less than 400 days are also associated with malignancy because nodules that grow rapidly over days to weeks are more likely to be infectious or inflammatory, and aggressive cancers can double in volume every three to four months (Table 2).⁷ Significant growth found on follow-up imaging is presumptive evidence of malignancy and requires consultation with a pulmonary subspecialist or more frequent monitoring. Subsolid nodules include pure ground-glass and part-solid nodules. Although less common than solid nodules (21% vs. 79% in one lung cancer screening study), part-solid nodules are associated with a higher risk of slow-growing cancer.⁹ Increasing age, greater than 20-pack-year smoking history among current smokers or those who have quit within the past 15 years, a family history of lung cancer, and exposure to asbestos, uranium, or radium are associated with an increased risk of pulmonary malignancy.³

What Is the Evidence for Screening Asymptomatic People for Lung Cancer?

The U.S. Preventive Services Task Force (USPSTF) recommends annual screening for lung cancer with low-dose computed tomography (CT) in adults 50 to 80 years of age who have a 20-pack-year smoking history and currently smoke or quit smoking within the past 15 years. Screening should be discontinued once a person has not smoked for 15 years or develops a health problem that substantially limits life expectancy or a willingness to have curative lung surgery (USPSTF Grade B recommendation).¹⁰

EVIDENCE SUMMARY

The National Lung Screening Trial compared annual low-dose CT to chest radiography for three consecutive years in patients at high risk (defined as 55 to 74 years of age with at least a 30-pack-year smoking history who were current smokers or had quit within the previous 15 years). After 6.5 years of follow-up, there was a 20% reduction in lung cancer–related mortality and a 6.7% decrease in overall mortality in the low-dose CT group.¹¹ A more recent meta-analysis of more than 96,000 people that included the National Lung Screening Trial data demonstrated that screening people at high risk with low-dose CT decreased lung cancer–related mortality by 1.8% to 2.2% over five to 10 years but did not change overall mortality.¹² In 2014, the USPSTF recommended the use of low-dose CT for lung cancer screening in people at high risk¹³; this recommendation was updated in 2021 based on data from additional studies and screening models showing benefits for a larger age range (50 to 80 years of age) and shorter smoking history (20-pack-year smoking history) and is endorsed by the American Academy of Family Physicians.^10,14 Screening patients at high risk of lung cancer with low-dose CT is also recommended by the American College of Chest Physicians (CHEST) and the American Cancer Society, with screening starting at 55 years of age for patients with a 30-pack-year smoking history who currently smoke or have quit within the past 15 years.^15,16