Prognostic contribution of non-predominant solid and micropapillary components in lung adenocarcinomas

Lung cancer is the leading cause of cancer-related mortality worldwide, and adenocarcinoma is the most common histological type of lung cancer. Most cases of lung adenocarcinomas have mixed histological patterns, which were histopathologically diagnosed as “adenocarcinoma, mixed subtype” in the World Health Organization (WHO) classification of 2004 (1). However, in 2011, the International Association for the Study of Lung Cancer (IASLC), American Thoracic Society (ATS), and European Respiratory Society (ERS) proposed a new classification in which major histological patterns (lepidic, acinar, papillary, solid, and micropapillary) and variants (mucinous, colloid, enteric, and fetal adenocarcinoma) were defined, and recommended that lung adenocarcinomas should be classified according to their predominant subtypes, after identification and quantification of all histological patterns in the tumor in 5% increments (2). This classification of lung adenocarcinoma was adopted in the new WHO classification in 2015 (3).