P2.17-22 Retrospective Analysis of Spread Through Air Spaces and Other Features in Patients with Stage IA Adenocarcinoma by the 8th TNM Classification

Abstract

We have recently demonstrated that the presence of the Spread Through Air Spaces (STAS) increased the risk of recurrence after resection for small lung adenocarcinoma (ADC). Currently, the TNM classification of lung cancer was revised and T-factor was changed to be basically determined by its invasive size. The purpose of this study is to examine the impact of presence of STAS in stage IA ADC according to the 8th TNM classification. Patients with pleural invasion, lymph node metastasis, distant metastasis, and neoadjuvant therapy were excluded. All available tumor slides from patients with surgically resected solitary lung ADC (2000-2015) were reviewed. Patients with stage IA ADC according to the 8th TNM classification were collected. Overall survival (OS) and recurrence-free probability (RFP) were estimated using the Kaplan-Meier method. Propensity score was generated from age, operation year, gender, lymphatic invasion, vascular invasion, the presence of solid component ≥5%, the presence of micropapillary component ≥5%, limited resection, and invasive size. One-by-one nearest neighbor matching by the presence of STAS was adapted to reduce the bias. In all, 295 patients met study criteria with median age of 68. Male gender comprised 48.8% (n=144), lymphatic invasion positive 4.7% (n=14), and vascular invasion positive 14.9% (n=44). By T-factor (7th edition), 216 (73.2%) were T1a, 53 (18.0%) T1b, 23 (7.8%) T2a, 2 (0.7%) T2b, and 1 (0.3%) T3. By T-factor (8th edition), 100 (33.9%) were T1mi, 111 (37.6%) T1a, 70 (23.7%) T1b, and 14 (4.7%) T1c. By operation method, 241 (81.7%) underwent lobectomy, 15 (5.1%) segmentectomy, and 39 (13.2%) partial resection. Adjuvant chemotherapy was given in 2.7% (n=8) of patients. STAS was seen in 22.7% (n=67) of patients. Five-year OS was 95.3% for STAS-negative and 91.1% for STAS-positive (p=0.0262), and the 5-year RFS was 96.8% and 83.9%, respectively (p=0.0003). In matched cohorts, each cohort included 48 patients and the 5-year OS was 95.0% for STAS-negative and 90.6% for STAS-positive (p=0.3201). The 5-year RFS was 93.3% and 91.3%, respectively (p=0.9363). Patients with pathologic stage IA ADC with STAS, according to the 8th TNM classification, had a worse prognosis in unmatched cohorts even though adenocarcinoma in situ was excluded. Because of various confounding factors, the propensity score matching revealed the presence of STAS as a non-significant prognostic factor in our matched cohorts. This study was a retrospective analysis, and a prospective study is needed regarding the indication of limited resection.