P3.01-022 Impact of Histologic Subtype and Spread through Air Spaces (STAS) in Stage III (N2) Lung Adenocarcinoma: Topic: Morphology

Abstract

Approximately 15% of patient with non-small cell lung cancer (NSCLC) is present with stage III (N2) disease. The patient prognosis after complete resection for pathological N2 NSCLC remains a significant concern. Currently, the new World Health Organization classification of lung cancers was revised and newly prescribed to describe the presence of each histologic subtype in adenocarcinoma (ADC) and the Spread Through Air Spaces (STAS). The purpose of this study is to examine the relationship between histologic subtype and patient outcome, especially for metastatic lymph node, and clinicopathologic features of STAS in stage III (N2) lung ADC according to new WHO classification retrospectively. All available tumor slides from patients with pathological N2, surgically resected lung ADC (1998-2013) were reviewed. Each tumor was evaluated by comprehensive histologic subtyping according to new WHO classification, and the percentage of each histologic component was recorded in 5% increments. We reviewed the histologic subtype in the N2 lymph nodes and relationship between main tumor and N2 lymph nodes. Recurrence-free probability (RFP) and overall survival (OS) were estimated using the Kaplan-Meier method. 78 patients met inclusion criteria (55% men; median age: 68yrs; 76 stageIIIA/2 stageIIIB, 77 lobectomy). The 5-year RFP and OS in N2 lung ADC were 27.8%, 66.8%, respectively. The histologic subtypes such as acinar, micropapillary and solid components in the main tumor were significantly seen in the N2 lymph nodes (P < 0.001, P < 0.05, P < 0.05, respectively). STAS was identified in 48 patients (61.5%) and significantly associated with recurrence (5-year RFP: 18.4% vs. 43.8%, P < 0.05). STAS was significantly associated with presence of micropapillary component (≥ 5%) and lymphatic invasion in the main tumor (P < 0.001). Presence of acinar, micropapillary and solid component in the main tumor are associated with metastasizing to lymph nodes. Presence of STAS was significantly associated with increased risk of recurrence in stage III (N2) lung adenocarcinoma.