The new 2011 international association for the study of lung cancer/american thoracic society/european respiratory society classification of lung adenocarcinoma in resected specimens: clinicopathologic relevance and emerging issues

Abstract

Pathologists play an increasingly important role in personalized medicine for patients with lung cancer as a result of the newly recognized relationship between histologic classification and molecular change. In 2011, the International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society (IASLC/ATS/ERS) proposed a new architectural classification for invasive lung adenocarcinomas to provide uniform terminology and diagnostic criteria. This review highlighted the evolution of the classification of lung adenocarcinomas in resected specimens with special respect to both histologic subtyping and invasion. Histologic subtyping of lung adenocarcinoma has been updated based on five major predominant patterns. New concepts of adenocarcinoma in situ and minimally invasive adenocarcinomas have been introduced to define the condition of patients who are expected to have excellent survival. Although the new IASLC/ATS/ERS classification has promising clinical relevance, significant clarification remains necessary for the definitions of subtyping and invasion. More precise definitions and subsequent better education on the interpretation of terminology will be helpful for future studies.

Keywords: Adenocarcinoma; Classification; Invasion; Lung; Subtyping.

Fig. 1

(A) Nonmucinous adenocarcinoma in situ. (B) Tumor shows continuous growth of neoplastic cells along the slightly thickened alveolar septa without disruption of the alveolar structures. (C) Equivocal invasion showing alveolar collapse. Tumor has a central scar (arrow) with a peripheral lepidic growth pattern. (D) The central scar demonstrates thick fibrous septa with intact tumor glands, but less identifiable alveolar architecture and plump, reactive fibroblasts. Some pathologists interpreted a desmoplastic stroma associated with tumor invasion, whereas others considered the same features as benign scarring/fibroelastosis in Thunnissen's reproducibility study. (E) Nonmucinous minimally invasive adenocarcinoma. Tumor consists predominantly of lepidic growth with a small invasion focus (arrow). (F) Tumor acini and single cells are invading in the desmoplastic stroma with chronic inflammatory cells.