Grey zones in respiratory cytology: Atypical or suspicious for malignancy and neoplasms of unknown malignant potential.

The purpose of pulmonary cytology is two-fold. First, to establish whether a pulmonary nodule is benign or malignant. Second, pulmonary cytology should classify the type of pathologic process present. When a pulmonary nodule is characterized as malignant, it is of high importance to further classify the malignancy as to type, with non-small cell carcinomas being sub-divided into adenocarcinomas, squamous cell carcinomas, and other types of non-small cell carcinoma. The World Health Organization Reporting System for Lung Cytopathology (WHORSLC) provides an important framework for reporting and classifying material obtained by cytologic techniques, including sputum analysis, bronchial brushings, bronchial washings, and fine-needle aspiration. The system contains five categories for specimen reporting. Clinicians prefer definitive diagnoses separating specimens into definitively benign or definitively malignant categories. The WHORSLC recognizes that it is not invariably possible for cytopathologists to separate specimens into definitively benign or definitively malignant categories. The five categories of the WHORSLC recognize the spectrum of cytologic changes running from clearly benign to clearly malignant, which cytopathologists must place into diagnostically useful and reproduceable categories. The intermediate categories of "atypical" and "suspicious for malignancy" provide structured categories with stringent definitions, estimated malignancy risks, and suggested management and follow-up recommendations. In this way, the categories "atypical" and "suspicious for malignancy" aid in maintaining the high diagnostic accuracy of the "benign" and "malignant" categories.