Cons: the confusing mucinous adenocarcinoma classification

In 2015 a new WHO classification of lung tumors was issued. This classification clarified several important issues and corrected many entities (1). For adenocarcinomas the previous published classification (2) was adapted and largely taken over. Adenocarcinomas are now grouped into non-mucinous adenocarcinomas and adenocarcinoma variants. Within the non-mucinous adenocarcinomas the evaluation of primary, secondary, and tertiary patterns have to be given in percentages; patterns recognized are lepidic, acinar, papillary, micropapillary, and solid. Recently cribriform pattern was added as another pattern conferring worse prognosis (3,4). Patterns are also important for prognosis, as lepidic pattern confers a good prognosis, whereas solid and micropapillary regardless of their percentage confers a worse prognosis.