Leading international pulmonary societies have jointly proposed a new classification for pulmonary adenocarcinoma in order to address limitations of the 2004 WHO classification system, which does not address new, predictive roles for molecular testing in management of lung cancer patients. The new classification is based on architectural growth patterns. It eliminates the subtype bronchioloalveolar carcinoma, classifies all former mucinous BACs as invasive mucinous carcinoma, and recognizes adenocarcinoma in situ and minimally invasive adenocarcinomas. It recognizes lepidic: acinar: papillary; micropapillary and solid growth patterns as well as multiple histologic variants of mucinous carcinoma.
Reporting in Arch Pathol Lab Med. 2011;135:1329-1334 , Se Hoon Kim and colleagues from Seoul Korea determine whether these newly proposed histologic subtypes of lung adenocarcinoma predict EGFR mutation status in a cohort of Korean patients. They show that a predominant micropapillary growth pattern or any lepidic component are significantly associated with EGFR mutation. Ten of 12 (or 83% of ) micropapillary predominant adenocarcinomas were positive for EGFR mutation. In contrast, clinical features including gender, age, tumor size, and pathologic stage do not predict EGFR status.
Based on this paper and other studies, one could rationally consider anti-EGFR therapy in tumors with insufficient tissue for molecular testing but with predominant micropapillary growth pattern or a lepidic component.
Shim HS et al. (2011). Histopathologic characteristics of lung adenocarcinomas with epidermal growth factor receptor mutations in the International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society lung adenocarcinoma classification.Arch Pathol Lab Med. 135(10):1329-34.
Editorial. Guy E.Nichols MD, PhD. .