Here, we present a case of a distal‐type bronchiolar adenoma (BA) of the lung. BAs are benign lung tumors characterized by nodular proliferation of bilayered bronchiolar‐type epithelium with a continuous layer of basal cells. This patient underwent S3 segmentectomy following detection by computed tomography (CT) scan of a gradually enlarging ground‐glass nodule (GGO) over a five month period. Nodule morphology and immunophenotype were consistent with those of distal‐type BA of the lung. An epidermal growth factor receptor ( EGFR ) exon 21 p.L858R missense mutation was identified which, to the best of our knowledge, is the first case to be reported of a common gene mutation associated with non‐small cell lung cancer (NSCLC) being found in a BA lesion. Following surgery, the patient remains relapse‐free. Key points Significant findings of the study Pathological assessment of a lung nodule confirmed a papillary tumor with a double‐layered cell structure, less than typical cytoplasm, and a mixture of ciliated columnar and globular cells, consistent with a distal‐type bronchiolar adenoma. What this study adds This is the first report of an EGFR exon 21 p.L858R mutation in a bronchiolar adenoma.
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