Terminal deoxynucleotidyl transferase-positive precursor cells in reactive lymphadenopathies: a clinicopathologic analysis.

[OBJECTIVE] In this study, we aimed to determine the frequency, distribution, and phenotype of terminal deoxynucleotidyl transferase (TdT)-positive precursor cells in reactive lymphadenopathies; clarify the clinical significance of this expression; and present new data to the existing literature.

[METHODS] We retrospectively reviewed 152 excisional lymph node biopsy specimens diagnosed as reactive lymphoid hyperplasia (January 2023 to April 2024). Slides were evaluated primarily by hematoxylin and eosin and TdT immunohistochemistry. Then, dual immune staining (TdT/CD3, TdT/CD5, TdT/CD20, TdT/CD79a, TdT/CD10, and TdT/CD34) was applied to determine the characterization of TdT+ cells. Clinicopathologic variables (age group, sex, site, and histologic pattern) were recorded and compared.

[RESULTS] The TdT+ cells were detected in 13 of 152 cases (8.5%). These cells were primarily localized in the interfollicular regions of the lymph nodes, in areas close to the high endothelial venules. The TdT+ cells were slightly larger than lymphocytes and were seen individually or in small clusters (<10 cells). It was determined that some TdT+ cells coexpressed CD10 and/or CD34 by double immunostaining (mean 5.36%, up to 12% of TdT+ cells), suggesting that these cells are compatible with the common lymphoid precursor phenotype. No coexpression with CD3, CD5, CD20, or CD79a was observed.

[CONCLUSIONS] Benign TdT+ precursor cells can occasionally be found in reactive lymphadenopathies. These cells may sometimes coexpress CD10 or CD34. Recognizing this pattern is important, as it helps avoid mistaking these benign cells for lymphoblastic lymphoma or leukemia.