Subcentimeter lung nodules stable for 2 years at LDCT: Long-term follow-up using volumetry

Background and objective Subcentimeter nodules without change in size during long-term follow-up period (for minimum 2 years) are assumed as benign lesions. However, the 2-year stability rule has not been fully verified so far and is still questionable. Thus, we aimed to retrospectively investigate long-term follow-up results for 2-year stable subcentimeter nodules at screening low-dose computed tomography (LDCT). Methods A total of 635 subjects having had follow-up LDCTs for the initial 2-year screening period and additional 3 years thereafter and having had non-calcified subcentimeter nodules were included. By using computed tomography (CT) nodule volumetry software, we measured interval changes in nodule volume. Results A total of 1107 subcentimeter nodules (1037 solid, 70 ground-glass opacity nodules (GGNs)) were detected at baseline CT. Of 1037 solid nodules, 1032 showed no growth during the initial 2-year and 5-year follow-up period. Fifty-nine GGNs were stable for initial 2 years, but two (3.4%) were later proved as adenocarcinomas. Among five solid nodules that showed growth during the initial 2-year follow-up period, one (20%) proved to be an adenocarcinoma, whereas four (36.4%) of 11 GGNs that demonstrated growth were diagnosed as lung cancers. Conclusions All solid subcentimeter nodules having initial 2-year stability at screening LDCT can be considered benign because none shows growth at further follow-up CT. On the other hand, subcentimeter GGNs have more chance of growth than solid nodules and need further follow-up CT for more than 2 years. All solid subcentimeter nodules demonstrating initial 2-year stability at screening low-dose CT can be considered benign owing to their no growth thereafter, whereas subcentimeter ground-glass opacity nodules still have possibility of growth even after 2-year stability and thus need further follow-up CT.