Breast Metastasis from Pulmonary Mucoepidermoid Carcinoma in a Male Patient: A Case Report.

Mucoepidermoid carcinoma of the lung is a rare salivary gland-type tumor with heterogeneous clinical behavior and the potential to mimic neoplasms arising in other organs. The purpose of this report is to describe an exceptionally uncommon presentation of pulmonary mucoepidermoid carcinoma manifesting as a breast metastasis in a male patient, a scenario that poses significant diagnostic challenges due to its rarity and its morphological resemblance to primary breast carcinoma. We evaluated the patient through clinical examination, cross-sectional imaging, endobronchial procedures, ultrasound-guided biopsy, immunohistochemistry, and molecular analysis, integrating these data to establish the diagnosis. Imaging revealed a primary lung mass and a second lesion in the left breast infiltrating the pectoralis muscle. Biopsy of the breast mass showed high-grade salivary gland-type mucoepidermoid carcinoma, clinically and radiologically suggestive of pulmonary origin. Because the lesion showed signs of impending ulceration, palliative surgical debulking was performed with good postoperative recovery. The patient subsequently began systemic therapy with gemcitabine. This case underscores the need for careful clinicopathologic correlation when evaluating atypical breast lesions and highlights the diagnostic value of molecular testing in distinguishing primary from metastatic salivary gland-type tumors. Recognizing such rare metastatic patterns is essential for appropriate therapeutic planning.