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

Abstract

<b>BACKGROUND.</b> 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. <b>OBJECTIVE.</b> The purpose of this article is to investigate the impact of a minor (≤ 10%) GGO component on the prognosis of clinical stage I NSCLC in comparison with pure-solid nodules. <b>METHODS.</b> This retrospective study included 382 patients (mean age, 60.8 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 ratio (CTR) of 0.9 to 1.0. Two radiologists independently assigned nodules to groups as either minor GGO (CTR, ≥ 0.9 and < 1.0) or pure solid (CTR = 1.0). 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. <b>RESULTS.</b> The two radiologists agreed for all nodules' classification into the minor-GGO (<i>n</i> = 106) or pure-solid (<i>n</i> = 276) groups. The mean CTR of the minor-GGO group was 0.93 ± 0.02 (SD) (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; <i>p</i> < .001) and total nodule diameter (2.89 vs 2.16 cm; <i>p</i> < .001). The minor-GGO group, in comparison with the pure-solid group, showed lower frequencies of visceral pleural invasion (6.6% vs 17.0%, <i>p</i> = .009) and pathologic lymph node involvement (4.7% vs 20.3%, <i>p</i> < .001), and <i>EGFR</i> mutation (71.6% vs 39.9%; <i>p</i> < .001). The minor-GGO group, in comparison with the pure-solid group, showed better 5-year RFS (83.4% vs 55.0%; <i>p</i> < .001) and higher frequency of better 5-year CSS (92.4% vs 76.4%, <i>p</i> = .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, <i>p</i> = .001) but not with the likelihood of CSS. <b>CONCLUSION.</b> 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. <b>CLINICAL IMPACT.</b> Radiologists encountering predominantly solid nodules on CT should carefully assess images for even a minor-GGO component given the favorable prognosis.