[Case 3. Sclerosing pneumocytoma: A diagnostic pitfall mimicking pulmonary adenocarcinoma]

We report the case of a 72-year-old non-smoking woman with a 2.4cm parenchymal nodule in the left lower lobe discovered incidentally. Fine-needle aspiration cytology demonstrated an atypical papillary lesion with a CK7+/TTF1+ immunohistochemical profile and negativity for CK20, PS100 and synaptophysin, initially suggesting a primary pulmonary adenocarcinoma. A left lower lobectomy was performed. Pathological examination of the surgical specimen revealed a sclerosing pneumocytoma, a rare benign tumor of adulthood. This case illustrates the difficulty of preoperative cytological diagnosis of this entity and the importance of recognizing its morphological and immunohistochemical features to avoid surgical overtreatment.