Cytodiagnostic aspects of lung adenocarcinoma manifesting with micropapillary pattern in sputum: a case report of potential diagnostic pitfall.

The micropapillary pattern of lung adenocarcinoma was discussed in the 2004 World Health Organization classification and is now proposed as a distinct pattern in the new International Multidisciplinary Classification of Lung Adenocarcinoma Guidelines. The micropapillary pattern is histologically characterized by papillary tufts lacking a central fibrovascular core and is associated with an unfavorable prognosis. Herein, we report the cytological features of lung adenocarcinoma with the micropapillary pattern in a sputum specimen. A 75-year-old woman presented with a productive cough, blood-tinged sputum, and some symptoms of upper respiratory tract infection. The initial impressions from her chest radiograph and computed tomography scan indicated pneumonia. However, the initial sputum cytology sample showed a few clusters of cells with abnormal three-dimensional structure, interpreted as adenocarcinoma. These cells were small and had minimal cytologic atypia, demonstrating a potential diagnostic pitfall. The following biopsy confirmed lung adenocarcinoma with the micropapillary pattern. Here, we describe this case and discuss the differential diagnosis of pulmonary entities exhibiting similar morphologies.