OA12.06 A Retrospective Analysis of Patients with Small Lung Adenocarcinoma (≤2cm) by New World Health Organization Classification

Abstract

We have recently demonstrated that the presence of the Spread Through Air Spaces (STAS) and the variety of histologic subtypes increase the risk of recurrence after resection for small lung adenocarcinoma (ADC). Currently, the new World Health Organization classification of lung cancers was revised and newly prescribed to describe the presence of each histologic subtypes and STAS. The purpose of this study is to examine the risk factor for recurrence other than TNM staging analyzing clinical information retrospectively. All available tumor slides from patients with clinical stage I, therapy-naive, surgically resected solitary lung ADC ≤2 cm in size (1998-2015) were reviewed. Each tumor was evaluated by comprehensive histologic subtyping, and the percentage of each histologic component was recorded in 5% increments. STAS was defined as the spread of tumor cells into air spaces in the lung parenchyma adjacent to the main tumor according to the WHO classification. Recurrence-free probability (RFP) was estimated using the Kaplan-Meier method. 354 patients met inclusion criteria (52.3% men; median age: 67yrs; median tumor size: 1.3cm; 325 stage IA/ 29 stage IB; 91 partial resection/ 22 segmentectomy / 241 lobectomy or pneumonectomy). The prognosis didn’t differ significantly between sublobar resection group and lobectomy or pneumonectomy group (5-year RFP: 88.4% (N=113) vs. 91.9% (N=241), P=.162). Presence of STAS was identified in 74 cases (20.9%) (36 Micropapillary pattern / 55 Solid pattern / 15 Single cells). STAS was significantly associated with recurrence (5-year RFP: 94.3% vs. 76.2%, P < .0001). Histologic subtypes were 62 adenocarcinoma in situ (18%), 110 minimally invasive adenocarcinoma (31%) and 182 invasive adenocarcinoma (51%). The recurrence after sublobar resection was seen in 13 cases (1 partial resection (4.5%) / 12 segmentectomy (13%), 5 STAS (+)/ 8 STAS (-), 6 solid predominant / 5 acinar predominant / 2 lepedic predominant, 5 pulmonary recurrence / 4 lymph node recurrence / 2 local recurrence / 2 others). Patients with solid component had significantly worse prognosis (5-year RFP: 71.7% (N=83) vs. 96.3% (N=271), P<.0001). Among them, patients with sublobar resection had significantly more recurrence than with lobectomy or pneumonectomy (5-year RFP: 51.4% (N=19) vs. 77.7% (N=64), P=.0021). The patients of small ADC with STAS or solid component had worse prognosis. The patients after sublobar resection with solid component should be made follow-up closely. We propose that the presence of those features should be considered a factor to upgrade the pathologically defined T stage.