Incidence rate and malignancy risk in new nodules in a lung cancer screening programme

There is limited evidence for the malignancy risk posed by new nodules appearing at annual screening rounds or at short-term interval nodule follow-up (NFU) CTs in lung cancer screening programmes. We investigated incidence rate and malignancy risk in new nodules appearing at NFU and at first annual CT in a screening cohort and investigated nodule and participant characteristics which predicted malignancy.

11,566 participants underwent baseline CT screening between April 2019 and April 2020. CTs were read in conjunction with computer-aided detection software with semi-automated volumetry. Nodule management was based on British Thoracic Society guidelines, with the addition of a lower threshold for new solid nodules appearing at incident rounds; those ≥ 30 and < 200 mm³ underwent a further 3-month interval scan, and new nodules ≥ 200 mm³ were referred directly for definitive investigation.

New nodules were identified in 8.4% of participants at NFU-CT and 11.1% at Y1. 0.63% (95% confidence interval (CI) 0.016-3.433) of new nodules at NFU-CT and 2.98% (95% CI 1.83-4.57) at annual CT proved malignant. Malignancy risk in new nodules at Y1 was 1.67% in nodules < 30 mm³, 2.2% in nodules 30-200 mm³ and 11.0% in nodules > 200 mm³. No nodules with typical perifissural or subsolid morphology were malignant. There was no significant difference in age, smoking status, smoking history or predicted cancer risk between participants with new nodules which proved malignant and those which were benign.

Our findings validate the need for lower volume thresholds for further surveillance or definitive investigation in new solid nodules at annual scans. Malignancy risk in new nodules with subsolid or typical perifissural morphology and in new nodules appearing in a shorter time frame of NFU CTs is low.

Question What is the incidence and malignancy risk of new nodules appearing at annual and nodule follow-up interval CTs in lung cancer screening? Findings New nodules were seen in 11.1% and 8.4% of participants at annual low-dose CT and 3-month interval CT, respectively. Malignancy risk at annual CT increased with nodule size. Clinical relevance In a lung cancer screening programme, new nodules at annual and nodule follow-up CTs occur in around 1 in 10 participants. Lower size thresholds for further surveillance or definitive investigation should be considered compared to nodules at baseline CT.