Spontaneous regression of mucosa-associated lymphoid tissue lymphoma of the lung

We report a case of mucosa-associated lymphoid tissue (MALT) lymphoma of the lung that regressed spontaneously. An 82-year-old man was referred to our hospital because of an abnormal chest shadow. Chest CT scans showed soft tissue components along the periphery of the left main bronchus. Bronchoscopy showed an edematous and protruding lesion. Pathological findings showed diffuse invasion of small lymphoid cells of B-cell origin in the submucosal layers. These cells formed lymphoepithelial lesions. Southern blot hybridization demonstrated monoclonality and immunoglobulin heavy-chain gene rearrangement. We diagnosed MALT lymphoma of the lung. Spontaneous regression was found clinically 16 days after the first tumor biopsy for diagnosis by bronchoscopy. Autofluorescence imaging (AFI) 8 months after the first biopsy showed a decrease in magenta color. Immunohistochemical staining showed marked decrease in CD20 + B cells and an increase in the proportion of T cells, the majority of which were CD4 + T cells. No relapse of these lesions was detected 20 months after the first visit. It may be possible to closely follow up pulmonary MALT lymphoma without immediate treatment.