Clinicopathologic study of primary thymic extranodal marginal zone lymphoma of mucosa associated lymphoid tissue and lymphoepithelial sialadenitis-like thymic hyperplasia / 临床与实验病理学杂志

ABSTRACT

Purpose To discuss the clinicopathological features of primary thymic extranodal marginal zone lymphoma of mucosa associated lymphoid tissue (MALT) lymphoma and lymphoepithelial sialadenitis (LESA)-like thymic hyperplasia,their relationship and differential diagnosis.Methods Three cases of thymic MALT lymphoma and one LESA-like thymic hyperplasia were evaluated by HE staining,immunohistochemistry and immunoglobulin (Ig) gene rearrangement technology.Results The symptoms of Sjsgren syndrome were found in the two patients with thymic MALT lymphoma.Microscopically,the normal architecture of thymus was effaced by dense lymphoid infiltration composed predominantly of centrocyte-like and monocytoid B cells with prominent lymphoepithelial lesions.Immunohistochemically,the tumor cells were positive CD20,PAX-5,and BCL-2.The plasma cells showed lambda light chain restriction in one case with prominent plasmacytoid differentiation.In LESA-like thymic hyperplasia,the normal lobular architecture of thymus was generally reserved and abundant lymphoid tissue containing lymphoid follicles was seen with prominent lymphoepithelial lesions in expanding islands of thymic epithelial cells and epithelium lining the cysts,but a monocytoid B-cell population was absent.Immunohistochemically,a mixed B-cell and T-cell population was identified.A monoclonal rearrangement of the Ig gene was detected in all three thymic MALT lymphomas but not in the case of LESA-like hyperplasia.Conclusion Primary thymic MALT lymphoma and LESA-like thymic hyperplasia are both rare lymphoid proliferative lesions and the two lesions have overlapping histological and immunohistochemical features.A combination of genetic rearrangement and analysis of the differential points is helpful to distinguish between them.