The WHO classification of lung tumours on which pathologists base their diagnosis was revised in 2015 on the basis of an international consensus established in 2011 between clinicians, radiologists and pathologists. This resulted in a histo-molecular and prognostic classification of adenocarcinomas. The use of immunohistochemistry for the classification of poorly differentiated non-small cell carcinomas and a new classification adapted to small specimens were defined. These concepts are still relevant today, as the management of small specimens is a key point in the collaboration between the sampling physician and the pathologist.
This classification was revised in 2021 and remains broadly the same except for the appearance of new entities: SMARCA4-defident undifferentiated thoracic tumour; bron-chiolar adenoma / muconodular ciliated papillar tumour. Although rare, these lesions have histopathological, clinical and/or molecular appearances that merit their presence as new entities.
For invasive adenocarcinomas, the 5 architectural patterns are maintained but the IASLC proposes a grading system which has shown a prognostic impact for early stages.
Some clarifications regarding the diagnosis of neuroendocrine tumours/carcinomas were provided.