Flow Cytometric Evaluation of Double/Triple Hit Lymphoma

"Double" or "triple" hit lymphomas (D/THL) with recurrent translocations involving MYC/8q24 and BCL2/18q21 and/or BCL6/3q27 are characterized by a poor prognosis, but their identification is hampered by the clinicopathologic overlap with other disease categories. Cases with circulating blastic-appearing cells may initially cause concern for lymphoblastic leukemia a diagnostic dilemma, which has not been well studied. There is only limited literature regarding the flow cytometric (FC) D/THL phenotype and its clinical correlates. The FC features of 20 D/THL (11 BCL2(+)/MYC(+), 5 BCL6(+)/MYC(+), 4 BCL2(+)/BCL6(+)/MYC(+)) were evaluated, compared to 20 B-lymphoblastic leukemias (B-LBL), and correlated with overall survival. Most (89%, 17/19) D/THL were CD10(+), 47% (9/19) lacked surface light chain, and a significant subset underexpressed CD45 (47%, 9/19), CD20 (42% 8/19), and/or CD19 (39%, 7/18), which did not vary by genetic subgroup. Compared to B-LBL, D/THL less frequently underexpressed CD45 (p = 0.0001) and CD20 (p = 0.0004). Lower levels of BCL2 expression were noted in the BCL6(+)/MYC(+) and BCL2(+)/BCL6(+)/MYC(+) subgroups versus BCL2(+)/MYC(+) cases (p = 0.0014). Of the flow cytometric parameters assessed, dim CD45 expression correlated with inferior survival (p = 0.01). Although there is some overlap with B-LBL, D/THL demonstrates a characteristic immunophenotype which may have prognostic significance and warrants further investigation.