Primary Lung Small B-Cell Lymphoma versus Lymphoid Hyperplasia: Evaluation of Diagnostic Criteria in 26 Cases.

Primary lung non-Hodgkin's lymphoma is a rare neoplasm mostly represented by low-grade B-cell lymphomas of mucosa-associated lymphoid tissue. Their diagnostic criteria are now well defined on surgical specimens, but pathologists may experience difficulties in distinguishing them on exiguous biopsies from benign lymphoid hyperplasia and other lymphomas. Therefore, we examined a series of 26 lung lymphoid lesions to further define the pathologic features of either lymphoma or lymphoid hyperplasia on small specimens. We observed 16 primary lung non-Hodgkin's lymphomas with a large predominance of low-grade mucosa-associated lymphoid tissue-type lymphomas (87.5%, n = 14). There were no autoimmune disorders, but three patients had a concomitant infectious disease (hepatitis C virus and Helicobacter pylori gastritis). One patient presented with a synchronous pulmonary adenocarcinoma. As well as the classical mucosa-associated lymphoid tissue cellular infiltrate, immunohistochemical characterization of the 14 mucosa-associated lymphoid tissue-type lymphomas revealed the CD20+/CD43+ centrocyte-like cell phenotype in 10 cases (71.5%). Although the lymphoepithelial lesions observed in all lymphomatous cases have been reported in lung lymphoid hyperplasia, the determination of B-cell CD20+/CD43+ phenotype of the intraepithelial lymphocytes highly increased the specificity of lymphoepithelial lesions. A monoclonal immunoglobulin heavy chain gene rearrangement was present in 71.4% of the mucosa-associated lymphoid tissue-type lymphoma specimens. Investigation of H. pylori by polymerase chain reaction detection was negative, even for the two cases associated with H. pylori gastritis.