Primary low-grade B-cell lymphoma in mucosa-associated lymphoid tissue of the lung.

A 67-year-old asymptomatic woman was referred to our department for treatment for a left lung tumor. The tumor was 40 mm in diameter and was present in the left lower lobe. A primary low-grade B-cell lymphoma in the mucosa-associated lymphoid tissue of the lung was suspected after a trans-bronchial lung tissue biopsy. Systemic screening revealed no other organ involvement, and the tumor was considered to be a primary lung tumor. A left lower lobectomy with hilar and mediastinal lymph node sampling was performed. Pathological examination revealed centrocyte-like cells that expressed CD20. These cells had invaded the bronchiolar epithelium to form lymphoepithelial lesions. The pathological diagnosis was confirmed to be primary low-grade B-cell lymphoma in the mucosa-associated lymphoid tissue of the lung. The origin of this tumor type in the lung is relatively rare.