Primary high-grade malignant epithelial–myoepithelial carcinoma of the lung: diagnostic pitfalls of a very rare lung malignancy

Epithelial-myoepithelial carcinoma (EMC) is an exceptionally rare primary lung malignancy arising from submucosal bronchial glands. We report a 55-year-old man with a large paravertebral left lower lobe mass in whom bronchoscopic biopsy suggested metastatic poorly differentiated carcinoma of possible prostatic origin. Clinical work-up revealed a concomitant prostate carcinoma; however, following multidisciplinary discussion, prostatic origin was excluded and the patient underwent left lower lobectomy with mediastinal nodal dissection. Final diagnosis was primary high-grade malignant EMC, confirmed by an extended immunohistochemical panel and EWSR1 rearrangement (22q12) detected by fluorescence in situ hybridisation (FISH). A prior CT scan, retrospectively reviewed, showed a segmental consolidation four years earlier misinterpreted as pneumonia. This case illustrates the major diagnostic pitfalls of pulmonary EMC-including the coincidental discovery of a second primary tumour-and the indispensable role of molecular profiling when morphology and immunohistochemistry are inconclusive.