Flow Cytometric Detection of the Double-Positive (CD4+CD8+)/PD-1bright T-Cell Subset Is Useful in Diagnosing Nodular Lymphocyte-Predominant Hodgkin Lymphoma

Context.-Nodular lymphocyte-predominant Hodgkin lymphoma (NLPHL) is characterized by neoplastic lymphocyte-predominant cells frequently rimmed by CD3(+)/CD57(+)/programmed death receptor-1 (PD-1)(+) T cells. Because of the rarity of lymphocyte-predominant cells in most cases, flow cytometric studies on NLPHL often fail to show evidence of malignancy. Objective.-To evaluate the diagnostic utility of PD-1 in detecting NLPHL by flow cytometry, in conjunction with the CD4:CD8 ratio and the percentage of T cells doubly positive for CD4 and CD8. Design.-Flow cytometric data obtained from cases of NLPHL (n = 10), classic Hodgkin lymphoma (n = 20), B-cell non-Hodgkin lymphoma (n = 22), T-cell non-Hodgkin lymphoma (n = 5), benign lymphoid lesions (n = 20), angioimmunoblastic T-cell lymphomas (n = 6) and T-cell/histiocyte-rich large B-cell lymphomas (n = 2) were analyzed and compared. Results.-Compared with the other groups, NLPHL showed significantly higher values in the following parameters: CD4:CD8 ratio, percentage of T cells doubly positive for CD4 and CD8, percentage of PD-1-positive T cells, and median fluorescence intensity of PD-1 expression in the doubly positive for CD4 and CD8 subset. Using a scoring system (0-4) based on arbitrary cutoffs for these 4 parameters, all 10 NLPHL cases scored 3 or higher, as compared with only 3 cases from the other groups, producing an overall sensitivity of 100% and a specificity of 96% (72 of 75). Two of the 3 outliers were non-Hodgkin lymphoma, and both showed definitive immunophenotypic abnormalities leading to the correct diagnosis. The remaining outlier was a case of T-cell/histiocyte-rich large B-cell lymphoma. Conclusions.-The inclusion of anti-PD-1 in flow cytometry is useful for detecting NLPHL in fresh tissue samples, most of which would have otherwise been labeled as nondiagnostic or reactive lymphoid processes.