Primary Pulmonary Mucosa-associated Lymphoid Tissue Lymphoma with the High Expression of IgG4

This is the first report describing primary pulmonary mucosa-associated lymphoid tissue (MALT) lymphoma with the high expression of IgG4. The histological findings were compatible with the diagnostic criteria for MALT lymphoma and IgG4-related respiratory disease (IgG4-RRD). An unfixed sample for Southern blotting was not obtained since computed tomography findings showed multiple lung cysts, which is rare in patients with MALT lymphoma. However, polymerase chain reaction using paraffin sections showed the clonality of the immunoglobulin heavy chain variable region gene rearrangement, confirming a diagnosis of MALT lymphoma. This is an instructive case in which primary pulmonary MALT lymphoma was histologically compatible with IgG4-RRD.