Clinical relevance of the new IASLC/ERS/ATS adenocarcinoma classification

In 2011, recommendations for a multidisciplinary classification of lung adenocarcinoma were published under the auspices of the International Association for the Study of Lung Cancer, the American Thoracic Society and the European Respiratory Society. The review was considered necessary due to emerging data on the radiological features, genetics and therapeutic approaches to lung adenocarcinoma, all underpinned by expanding the knowledge of the pathology of this common tumour. The existing WHO classification of 2004 was not really fit for this multidisciplinary focus on the disease. This review describes the recommendations made on the reporting of surgically resected lung cancers according to their predominant pattern, and argues the case for replacing the term bronchioloalveolar carcinoma (WHO 1999 and 2004 definition) with adenocarcinoma in situ and for the introduction of minimally invasive adenocarcinoma. There is also a discussion of diagnosis of non-small-cell lung carcinomas in the small biopsy or cytology setting, a practice that was inadequately addressed in WHO 2004, yet this is much more relevant to most pathologists' daily practice because 85% or so of adenocarcinomas are never resected. Predictive immunohistochemistry, used correctly, can reduce non-specific diagnosis to less than 10% of the cases. Finally, there is an overview of the emerging data on therapeutically relevant lung adenocarcinoma genetics, considering targetable mutations that are now the focus of much activity. The clinical relevance of these changes is discussed.