CD10 expression in extranodal dissemination of angioimmunoblastic T-cell lymphoma

Angioimmunoblastic T-cell lymphoma (AITL) is a systemic disease that often has evidence of extranodal involvement at presentation. In a recent study of lymph nodes in AITL, we showed that the neoplastic T cells in most cases can be identified by aberrant expression of CD10. The aim of this study was to investigate whether CD10 expression by the neoplastic T cells is maintained in extranodal sites. Ten cases of AITL with histologic and immunophenotypic evidence of extranodal dissemination were studied. Seven cases of peripheral T-cell lymphoma unspecified (PTLu), that included biopsies of involved extranodal sites, two cases of enteropathy type T-cell lymphoma (ETTL), and one case of extranodal NK/T lymphoma, nasal type were selected as controls. Diagnostic lymph node biopsies and biopsies of extranodal sites were reviewed. PCR for T-cell clonality and single layer immunostaining for CD3, CD20, CD10, and CD21 and double layer immunostaining for CD20/CD10 were performed. All 10 cases of AITL had characteristic histologic features and molecular evidence of the disease in lymph node biopsies. In these cases, aberrant CD10 expression was maintained in the lung, cecum, tonsil, nasopharynx, and one of six involved bone marrow trephines. In these extranodal biopsies, the distribution of CD10-positive tumor cells correlated with that of the follicular dendritic cell meshwork (FDC). The five bone marrow trephines that lacked aberrant CD10 expression were devoid of morphologic and immunohistochemical evidence of FDC. In these five cases, there was evidence of aberrant CD10 expression in other involved sites that had FDC. The neoplastic cells in PTLu, ETTL, and extranodal NK/T lymphoma, nasal type were CD10 negative. Our data show that aberrant CD10 expression is a useful phenotypic marker for diagnosis of AITL in most involved extranodal sites, except bone marrow, and suggest a possible role of FDC in the pathogenesis of AITL.