Presence of immunoglobulin heavy chain rearrangement in so-called "plasma cell granuloma of the lung"

Inflammatory pseudotumor of the lung appears to be a set of heterogeneous disorders. Histologically, three subtypes of pulmonary IPTs have been delineated. Among these, plasma cell granuloma (PCG) is characterized by prominent lymphoplasmacytic infiltration, and PCG has been added to the list of differential diagnostic problems of mucosa-associated lymphoid tissue (MALT) type lymphoma. To investigate the presence or absence of monoclonal B-cell proliferation, we analyzed the immunohistological and genotypic findings in three cases of pulmonary PCGs. Histologically, the three lesions were characterized by severe infiltration of mature plasma cells, plasmacytoid cells, and small lymphocytes intermixed. Scattered Russell bodies (intracytoplasmic inclusions) were present in all three cases, but there were no Dutcher bodies (intranuclear inclusions) or centrocyte-like cells. Immunohistochemical studies of light chain determinants demonstrated the polytypic nature of B-cells. There was no CD5(+), CD43(+) or cyclin D1(+) B-lymphocytes in any of the three lesions. There were no lymphoepithelial lesions detected within any of the three lesions even by immunostaining for cytokeratin. However, polymerase chain assay for immunoglobulin heavy chain gene demonstrated a clonal band in one of the three cases. It currently remains unclear whether this one case, demonstrating IgH gene rearrangement in our series, could be a sign of the prelymphomatous stage (e.g. incipient MALT type lymphoma) or merely represents an exaggeration of normal B-cell clonal response.