Primary Pulmonary Epithelial-Myoepithelial Carcinoma With Prominent Reactive Pneumocytes: Clinicopathological Insights Into a Rare Case and Literature Review.

Primary salivary gland-type tumors may rarely be accompanied by hyperplastic alveolar cells, a pattern referred to as pneumocytic adenomyoepithelioma (PAM). Most previously reported cases have relied solely on immunohistochemical findings. In this report, we present a case involving three distinct types of epithelial cell components, identified through dual immunohistochemical staining for p40/TTF-1, in addition to the detection of HRAS mutation using next-generation sequencing. The female patient, in her 70s, underwent left lower lobectomy after a chest CT scan revealed a 20 mm solid mass in the left lower lobe. The final histopathological diagnosis was a primary pulmonary epithelial-myoepithelial carcinoma (EMEC). This paper presents a case of a primary pulmonary EMEC exhibiting so-called PAM morphology and includes a brief review of the literature.