Risk assessment of persistent incidental pulmonary subsolid nodules to guide appropriate surveillance interval and endpoints

Guidelines for the follow-up of pulmonary subsolid nodule (SSN) vary in terms of frequency and criteria for discontinuation. We aimed to evaluate the growth risk of SSNs and define appropriate follow-up intervals and endpoints. The immediate risk (IR) and cumulative risk (CR) of SSN growth were assessed using the Kaplan-Meier method according to nodule consistency and size. Follow-up plans were proposed based on optimal growth risk threshold of 5%. 892 SSNs, comprising 833 pure ground-glass nodules (pGGNs) and 59 part-solid nodules (PSNs) were included. For pGGNs ≤ 6.6 mm, the CR exceeded 5% at every 3-year interval in the first 9 years. For pGGNs measuring 6.6-8.8 mm and >8.8 mm, the IR remained above 5% for the first 2-7 years, and the 2-year CR for pGGNs measuring 6.6-8.8 mm in the 8th and 9th years achieved 6.66%. For PSNs, the IR peaked in the 4th year (44%) and then declined. Therefore, triennial follow-up for 9 years is recommended for pGGNs ≤ 6.6 mm, annual follow-up for 7 years followed by biennial follow-up for 2 years for pGGNs measuring 6.6-8.8 mm, annual follow-up for 7 years for pGGNs > 8.8 mm, and continuous annual follow-up until nodule growth for PSNs.