Prognostic role of subsolid ground-glass opacity, pure ground-glass opacity, and solid nodules of the lung: a retrospective observational study.

Background: Lung nodules can be classified as solid nodules and ground-glass opacity nodules (GGO-GGN). A GGO nodule is a radiological finding characterized by a faded opacity that may hide a preinvasive or invasive adenocarcinoma. GGOs can be divided into two categories: pure GGO (pGGN) and mixed/subsolid GGO (mGGN). The transformation of GGO into solid nodules is a strong indicator of malignancy. Current guidelines suggest a 5-year chest computed tomography (CT) follow-up (FU) for both pure and subsolid GGOs. This study aimed to analyze the prognosis of patients undergoing major lung resection at our center in relation to the radiological characteristics of the resected nodule to assess how much the nodule density in GGO may affect the prognosis.

Methods: This retrospective observational study analyzed 133 patients underwent lobectomy at our center between 2010 and 2020. The nodule density was assessed by CT images, classifying into three groups according to the consolidation tumor ratio (CTR): group 1: pure GGO (pGGN; CTR <0.5, n=30); group 2: subsolid nodule (mGGN; 0.5≤ CTR <1, n=37), group 3: solid nodule (CTR =1, n=66). Overall survival (OS) was calculated from the date of surgery until death or last FU. The OS was estimated through Kaplan-Meier curves, the log-rank test was used for univariate analysis, and Cox regression was used for multivariate analysis. Values with P<0.05 were considered statistically significant.

Results: Of 133 patients, the OS, 5 years after surgery and related to the nodule density, has been classified into three groups as: group 1 contained 30 patients with pure GGO nodules, with a 5-year survival rate of 96% [95% confidence interval (CI): 73-99%]; group 2 contained 37 patients with subsolid GGOs, with a 5-year survival rate of 76% (95% CI: 56-88%); group 3 contained 66 patients with solid nodules, with a 5-year survival rate of 78% (95% CI: 62-88%) with median survival time was 95 months. Multivariate analysis with age and FU lasting for over 6 months in the Cox model confirmed that density was a risk factor, with hazard ratio (HR) =8.37 (95% CI: 1.03-68.12) for group 2 vs. group 1 and HR =8.66 (95% CI: 1.06-70.90) for group 3 vs. group 1. A FU exceeding 6 months after diagnosis was not a significant risk factor (P=0.57), whereas age was a significant risk factor (HR =1.07, 95% CI: 1.001-1.13).

Conclusions: For pure GGO long-term FU is justified, whereas surgery should be considered as the first option for subsolid nodules. This retrospective study provides a foundation for further research to better define the most appropriate approach to subsolid nodules.