Minor (≤ 10%) Ground-Glass Opacity Component in Clinical Stage I Non-Small Cell Lung Cancer: Associations With Pathologic Characteristics and Clinical Outcomes.

ABSTRACT

Background: The presence of a ground-glass opacity (GGO) component is a favorable prognostic factor in non-small cell lung cancer (NSCLC), although the prognostic impact of a very small GGO component remains poorly investigated. Objective: To investigate the impact of a minor (≤10%) GGO component on the prognosis of clinical stage I NSCLC in comparison with pure-solid nodules. Methods: This retrospective study included 382 patients (mean age, 61 years; 210 men, 172 women) who underwent surgical resection between January 1, 2015 and December 31, 2015 for clinical stage I NSCLC appearing on preoperative chest CT as a nodule with a consolidation-to-tumor (CTR) ratio ≥0.9 and <1.0. Two radiologists independently assigned nodules to a minor-GGO (≥0.9 CTR <1.0) or pure-solid (CTR=1.0) groups. Recurrence-free survival (RFS) and cancer-specific survival (CSS) were assessed by Kaplan-Meier curves and compared between groups using log-rank tests. Cox proportional hazards models were used to assess associations with outcomes. Results: The two radiologists agreed for all nodules' classification into the minor-GGO (n=106) or pure-solid (n=276) groups. The mean CTR of the minor-GGO group was 0.93±0.02 (range, 0.90-0.97). Minor-GGO nodules, in comparison with pure-solid nodules, showed greater solid component diameter (2.68 vs 2.16 cm, p<.001) and total nodule diameter (2.89 vs 2.16 cm, p<.001). The minor-GGO group, in comparison with the pure-solid group, showed lower frequencies of visceral pleural invasion (6.6% vs 17.0%, P=.009), pathologic lymph node involvement (4.7% vs 20.3%, P<.001), and epidermal growth factor mutation (71.6% vs 39.9%; P<.001). The minor-GGO group, in comparison with the pure-solid group, showed better 5-year RFS (83.4% vs 55.0%; P<.001) and better 5-year CSS (92.4% vs 76.4%, P=.004). In multivariable analysis adjusting for patient, imaging, pathologic, and genetic factors, a minor-GGO component was independently associated with a decreased likelihood of recurrence (HR=0.37, P=.001) but not with the likelihood of CSS. Conclusion: Among patients with clinical stage I NSCLC, cancers with a minor-GGO component were associated with a better prognosis versus those with a pure-solid appearance. Clinical Impact Radiologists encountering predominantly solid nodules on CT should carefully assess images for even a minor-GGO component given the favorable prognosis.