The "drunken honeycomb" feature of pulmonary mucinous adenocarcinoma: a diagnostic pitfall of bronchial brushing cytology.

Pulmonary mucinous adenocarcinoma (PMA) is the terminology recently proposed in the new International Association for the Study of Lung Cancer/American Thoracic Society/European Respiratory Society (IASLC/ATS/ERS) International Multidisciplinary Classification of Lung Adenocarcinoma Guidelines for most tumors previously classified as mucinous bronchioloalveolar carcinomas (mBACs). PMA is histologically characterized by lepidic growth and at least some degree of invasive growth of goblet or columnar neoplastic cells with abundant intracytoplasmic mucin. We report here the cytologic features of PMA in a bronchial brushing specimen. The patient is an 84-year-old woman with a persistent dense consolidation in the right middle lobe of the lung found on non-contrast computed tomography (CT) scan. Bronchial brushing smears showed a monotonous population of columnar neoplastic cells forming "drunken honeycomb"-like cell clusters. The neoplastic cells displayed inconspicuous cytologic atypia. The concurrent transbronchial tissue biopsy and the resection specimen confirmed the diagnosis of PMA. Due to the bland nuclear features, the neoplastic cells in the bronchial brushing specimen were interpreted as benign at the time of the initial diagnosis, demonstrating a diagnostic pitfall of bronchial brushing cytology. A high index of suspicion is recommended when a lung lesion with "drunken honeycomb"-like cell clusters is encountered in bronchial brushing specimens. The review of the literature regarding the recently designated PMA is presented.