Prognostic considerations of the new World Health Organization classification of lung adenocarcinoma

The 2015 World Health Organization (WHO) lung adenocarcinoma classification divides tumours into categories of indolent pre-invasive, minimally invasive and predominantly lepidic and, by examining predominant patterns of invasion, allows for further stratification into intermediate and high-grade tumours. The impact of the 2015 classification on prognosis was reviewed by a PubMed search for search terms “adenocarcinoma”, “lung pathology” and “prognosis” and relevant publications reviewed. These were sorted for data on stage and survival as impacted by histological classification, and survival studies were separated into all stage versus stage 1 studies. Predictive aspects of histological classification were also examined, but molecular correlates were not. The separation of adenocarcinoma in situ and minimally invasive adenocarcinoma from invasive subtypes as distinct prognostic entities and the prognostic significance, for disease specific and overall survival for low- and high-grade categories, are discussed. The impact on stage at presentation including risk of node metastasis by histology is examined, as well as histology in relation to recurrence after surgery. Early data with regard to the value of predominant histology in the prediction of chemotherapy response will also be explored.