Lung cancer is an uncommon development in the two years following the incidental detection of lung nodules, US research shows.

A study of incidental findings on CT scans found that even multiple nodules were not associated with a subsequent lung cancer diagnosis, suggesting that a more intensive surveillance strategy for these individuals was not warranted.

The retrospective cohort study comprised adults >18 years with lung nodules of any size incidentally detected by chest computed tomography between 2005 and 2015.

Patients who underwent the CT for lung cancer screening or surveillance and those with radiological evidence of lung cancer were excluded from the study.

The patients had a mean age of 67 years and almost a third of patients (31%) had a history of non-lung malignancy.

The study, published in Chest [link here], found 43% of patients had a single nodule and 57% had multiple nodules. Median and mean nodule sizes were 5.6 mm and 7.3 mm, respectively.

It found that 3.7% of patients with incidentally detected nodules subsequently developed lung cancer during the 2-year follow-up.

“The 2-year probability of lung cancer was higher than the overall population mean for individuals who had ever smoked (5.5%, 95%CI 4.9%-6.3%), with nodules >10mm to ≤20 mm (12.3%, 95%CI 10.5%-14.5%), with nodules >20mm to ≤30 mm (25.3%, 95%CI 20.6%-30.5%), or with upper lobe nodules (5.3%, 95%CI 4.5%-6.2%),” it said.

However the probability of lung cancer did not vary by sex, BMI, history of a prior non-lung malignancy, nodule number or laterality, or year of nodule diagnosis.

A multivariable analysis revealed that men (RR 1.51), individuals who have ever smoked (RR 3.22), and upper lobe nodule location (RR 1.67) were associated with a higher 2-year probability of lung cancer.

“Novel findings include non-linear relationships between lung cancer and age and BMI, and no association between lung cancer and a history of a prior non-lung malignancy or number of nodules,” it said.

The investigators said their findings of no association between a history of prior non-lung malignancy and the risk of lung cancer was in contrast to other studies.

“However, the absence of a relationship may be confounded by the type of prior non-lung malignancy, stage at presentation, and disease-free interval. Until additional evidence about the relationship between a prior non-lung malignancy and lung cancer becomes available, the complexity of care will remain high for this sizeable segment of the population of individuals with incidentally detected lung nodules.”

They recommended patient referral to a multidisciplinary nodule clinic or subspecialist.