A case of mucous gland adenoma of lung: a benign mimicker of malignancy

Abstract

Introduction: Mucous gland adenoma of the lung (MGA) is an uncommon benign tumor. MGA of lung is extremely rare with less than 70 cases documented in the literature to the best of our knowledge. At present, according to the World Health Organization's classification of thoracic tumors, MGA is categorized as epithelial tumor and subclassified under adenomas. This is characterized by endobronchial growth of mucous cells with no atypia. We report a case of MGA of lung which was clinical-radiologically suspected to be a malignant tumor and discuss the diagnostic approach, differential diagnosis, treatment and need for close follow-up, with a thorough review of the literature.

Case presentation: A 57-year-old lady presented with pain in the left chest wall and arm for a duration of 3 months. After clinical examination, an x-ray showed collapse, and consolidation on ipsilateral lung. The subsequent CT scan of the thorax showed an 14 x 12 x 11 mm lesion in the proximal left main bronchus. Clinico-radiologically, carcinoma of lung was suspected. The patient underwent endoscopy and the endobronchial biopsy from the lesion showed features of a papillary glandular neoplasm. There was no immunostaining of the lesional cells for TTF1, synaptophysin, chromogranin, and p40, with a low Ki67 index of <5%. Although the possibility of malignancy was deemed unlikely, resection was suggested for confirmation. The patient then underwent pneumonectomy on which a histological diagnosis of mucous gland adenoma was made. The patient is well and on follow-up for 12 months.

Discussion: Due to its rarity and clinical presentation mimicking malignancy, MCA presents challenges in diagnosis. Malignant entities like invasive mucinous adenocarcinoma, low-grade mucoepidermoid carcinoma, and endobronchial metastasis from extraneous sites need to be considered in the differential diagnosis.

Conclusion: Mucous gland adenoma of lung is a rare tumour; this case report highlights the challenges faced while reporting small biopsy samples of lung and the need to be aware of the benign mimickers of malignancy. For the accurate diagnosis of this rare entity, a multimodality approach that includes histological examination, immunohistochemical analysis and radiological findings is key.