MA10.05 Proposals for the Novel Clinical T Categories Based on the Presence of Ground Glass Opacity Component in Lung Adenocarcinoma

Abstract

In lung adenocarcinomas, the histologic lepidic growth pattern tends to correlate with the ground glass opacity (GGO) component, while solid components correspond with invasive adenocarcinoma. The Eighth edition of the TNM staging system suggests that the tumor size be determined according to the invasive size excluding the lepidic component. However, this new concept causes fatal confusion, i.e., tumors are classified into a same T category despite the part-solid or pure-solid appearances provided they showed a same solid component size. Between 2008 and 2012, we retrospectively evaluated 719 surgically resected cN0 lung adenocarcinomas that measures 30mm or less in total dimension to assess the prognostic impact on the presence of GGO among the Eighth TNM classification. According to the new T category, it was defined based on the solid component size as follow: Tis; 0 cm (pure-GGO), T1mi; ≤ 5 mm, T1a; 6-10 mm, T1b; 11-20 mm, T1c; 21-30mm. Furthermore, all tumors were classified into 2 groups, i.e., GGO or Solid arms based on the presence of GGO component. Of the cases, 133 (18%) were categorized in Tis, 88 (12%) in T1mi, 121 (17%) in T1a, 244 (34%) in T1b and 133 (19%) in T1c, respectively. Multivariate analysis revealed that both a presence of GGO and solid component were independently significant prognostic factors (p=0.007, 0.002). The 5y-overall survival (OS) was 99.2% in Tis, 95.8% in T1mi, 96.5% in T1a, 81.8% in T1b and 66.4% in T1c (p=0.038) with a median follow-up period of 56 months. When we evaluated the impact of T category based on GGO presence, the 5y-OS was significantly different between GGO and Solid arm in each T categories (T1a; 99.0% vs. 95.7%, p=0.045, T1b; 89.8% vs. 73.3%, p=0.004, T1c; 90.0% vs. 62.6%, p=0.046). Furthermore, clinical T categories significantly separated the OS in Solid arm (p=0.015) (T1a vs. T1b; p=0.090, T1b vs. T1c; p=0.037). In contrast, the 5y-OS was approximately 90% or more in GGO arm despite their T categories. Moreover, regarding radiological and pathological correlations, the rates of AIS was only 65% in Tis, and 51% showed invasive adenocarcinoma even in T1mi. Clinical T category should be considered based on the presence of GGO on thin-section CT, and tumor size should be applied exclusively to radiological solid lung cancer. In contrast, oncological outcomes of the tumor with GGO component were excellent despite their T categories, which should be described as Tis for pure-GGO, and T1a for part-solid tumor.