A Case of Mucous Gland Adenoma of the Lung Representing <scp>NKX3</scp> .1‐Positive Lung Tumour Spectrum

Mucous gland adenoma (MGA) is a rare, benign lung tumour. Recently, NKX3.1 immunohistochemistry was reported to be a diagnostic marker for distinguishing MGA from other mucinous tumours. A 60-year-old male with a 20-year history of a tumor-like lesion, primarily composed of mucus in the left lingual region. While the lesion was being monitored, its size gradually increased. We then performed a segmentectomy of the lingula. Postoperative pathological examination showed that the tumour had a tubulopapillary structure. The tumour cells were columnar with slight atypia, diffusely positive for NKX3.1 and were diagnosed as MGA. No recurrence was found after 6 months of postoperative follow-up, and the sputum count had markedly decreased. This case report aids in elucidating the pathogenesis of MGA and NKX3.1-positive lung tumours.