Angioimmunoblastic T-cell lymphoma in bone marrow: a morphologic and immunophenotypic study.

Angioimmunoblastic T-cell lymphoma is known to frequently involve bone marrow. However, the histologic and immunophenotypic features of angioimmunoblastic T-cell lymphoma at this site are poorly defined. We assessed 27 bone marrow specimens involved by angioimmunoblastic T-cell lymphoma from 20 patients. Histologically, bone marrow involvement was predominantly multifocal (74%) and exhibited a nodular pattern (78%), often associated with other patterns. Using immunohistochemistry, programed death-1 and CD10 were expressed by atypical lymphocytes in 17 (85%) of 20 and 5 (18.5%) of 27 specimens, respectively. CXCL13 was not expressed by atypical lymphocytes in all cases but did stain stromal cells consistent with follicular dendritic cells in 1 case. BCL-6 as a single antibody was difficult to interpret because many normal bone marrow cells are dimly positive, but BCL-6/CD3 dual staining highlighted BCL-6+ T-cells in all cases assessed. Antibodies specific for CD21 and CD35 did not highlight follicular dendritic cells in any biopsy specimens. Flow cytometry immunophenotyping revealed a CD3+CD10+ T-cell population in 2 (25%) of 8 cases assessed. We conclude that the recognition and classification of angioimmunoblastic T-cell lymphoma in bone marrow are made difficult by the uncommon expression of CD10 (25%), rarity of follicular dendritic cells, and lack of CXCL13 expression at this site. This is most likely attributable to the very different microenvironment of the bone marrow relative to lymph nodes and, in particular, the absence of follicles in bone marrow. By contrast, programed death-1 immunohistochemical staining and double labeling using antibodies specific for BCL-6 and CD3 were helpful in appreciating the follicular T-helper cell immunophenotype of angioimmunoblastic T-cell lymphoma.