A Rare Case of Small Cell Lung Carcinoma Diagnosed with a Breast Mass

A 63-year-old woman presented to the emergency department with dyspnea, chest pain, and a palpable right breast mass. Non-contrast thoracic computed tomography (CT) scan revealed suspicious lesions in the right upper lung lobe and right breast, as well as right pleural effusion. For further evaluation, ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT scan was performed. There was increased FDG uptake in the right breast, right lung, liver, bones, and lymph nodes. Histopathological assessment confirmed that the breast mass was a metastatic lesion originating from a primary small-cell lung carcinoma. The manifestation of primary lung carcinoma with a metastatic mass lesion in the breast region is a rare condition. The manifestation can lead to diagnostic challenges, particularly when distinguishing it from a primary breast tumor. ¹⁸F-FDG PET/CT may provide valuable information for staging and surveillance, especially in patients with atypical metastatic patterns. This case highlights that unexpected metastatic sites can significantly affect treatment strategies and are frequently associated with worse prognosis.