[The new classification of lung adenocarcinoma]

The new, interdisciplinary IASLC/ATS/ERS classification of lung adenocarcinoma has achieved a considerable impact since its publication in the year 2011. It separates tumours into preinvasive, minimally invasive and invasive subtypes. The preinvasive lesions atypical, adenomatous hyperplasia (AAH) and adenocarcinoma in situ (AIS) together with the minimally invasive adenocarcinoma (MIA), have an excellent prognosis after complete resection with 100 % survival. It enables a reproducible tumour grading by the determination of the predominant histological growth pattern which could be confirmed in several follow-up studies. Thereby the mixed subtype was eliminated which formerly represented about 80 % of all adenocarcinomas. Similarly, the terms bronchioloalveolar adenocarcinoma and bronchioloalveolar tumour growth were eliminated because they represented several distinct entities, specifically the in-situ lesions AAH and ACIS as well as the non-in-situ/invasive tumours like minimally invasive adenocarcinoma, lepidic predominant adenocarcinoma (LPA) and invasive mucinous adenocarcinoma (IMA). Although the classification is based on data from tumour resections it accommodates the fact that most tumours are diagnosed on biopsies and cytological specimens and includes recommendations for an efficient work-up to preserve tissue for molecular testing. Furthermore, the morphological analysis may provide hints for molecular changes including mutations with therapeutic relevance that may enable targeted molecular diagnostics. This review presents essentials facts of the new classification that will be part of the next WHO classification of lung tumors and its follow-up publications.