Peripheral pulmonary papillary adenocarcinoma with prominent cilia: report of a rare case that was difficult to diagnose preoperatively.

In pulmonary cytology, the existence of cilia is considered cytologic evidence of benign cells because it is generally considered that cilia could not be identified by light microscopic observation of pulmonary adenocarcinoma. However, we encountered a rare exceptional case of pulmonary adenocarcinoma with cilia.A 55-year-old woman with bloody sputum was admitted. Computed tomography revealed a lung tumor. Although transbronchial brushing cytology showed atypical cells suggestive of malignancy, some atypical cells had cilia, so we could not diagnose them as cancer cells. After antibiotic therapy, the tumor was surgically excised. Imprint cytology showed similar atypical ciliated cells. Histologically, the tumor was diagnosed as papillary adenocarcinoma with cilia and diffuse pleural dissemination was observed. Electron microscopic observation identified cilia. The patient died due to aggravation of cancer, which was confirmed on autopsy.This rare case of peripheral pulmonary papillary adenocarcinoma with cilia could not be diagnosed as cancer cell on cytology. Pulmonary papillary adenocarcinoma with cilia should be considered in the differential diagnosis of atypical cells in pulmonary cytology.