Malignant lymphoma of bronchus‐associated lymphoid tissue (BALT) coexistent with pulmonary tuberculosis

A case in which malignant lymphoma occurred in association with a tuberculosis focus in a 70-year-old man is reported. Surrounding the epithelioid cell granulomas with caseous necrosis was a dense and diffuse monotonous infiltration of atypical lymphoid cells. Acid-fast bacilli were found in the granulomas and pulmonary tuberculosis was diagnosed. The infiltrating atypical lymphoid cells occasionally invaded the respiratory epithelium producing lymphoepithelial lesions. Immunohistochemically, the lymphoid cells were positive for CD20, and clonal rearrangement of the immunoglobulin heavy chain gene was demonstrated by polymerase chain reaction (PCR). We diagnosed the lesion as a pulmonary malignant lymphoma of bronchus-associated lymphoid tissue (BALT) occurring in the background of tuberculosis. This is the first reported case of pulmonary BALT lymphoma coexistent with pulmonary tuberculosis.