[New WHO Reporting System for Lung Cytopathology]

The new WHO Reporting System for Lung Cytopathology (World Health Organization Reporting System) is an international and standardized reporting system for cytology of the respiratory tract. Five diagnostic categories are defined: "insufficient/inadequate/non-diagnostic", "benign", "atypical", "suspicious for malignancy", "malignant". The WHO Reporting System is intended to be also applicable in countries with limited resources. Therefore, classification into the five diagnostic categories is based upon cytomorphology. The key diagnostic cytopathological features are described in the WHO Reporting System and differential diagnoses and ancillary testing are also covered, especially immunocytochemistry and molecular pathology.