Hodgkin Lymphoma and Anaplastic Variants of Non-Hodgkin Lymphoma

Background and Objectives: Classic Hodgkin lymphoma (CHL), anaplastic large cell lymphoma (ALCL) and some cases of diffuse large B cell lymphoma (DLBCL) have overlapping morphologic features. Since they all represent distinct clinico-pathologic entities, we explored the differential diagnostic impact of immunophenotyping to discriminate between them. Materials and Methods: We included 61 cases diagnosed as CHL, ALCL, and anaplastic variant of DLBCL. We reviewed morphologic microscopic findings by conventional staining and immunohistochemistry (IHC) with antibodies against PAX-5, CD30, CD15, CD45, EMA, ALK-1, and LMP-1. Results: Fifty cases corresponded to CHL (81.97%), 4 cases to ALCL (6.56%), and 4 cases to DLBCL (6.56%) excluding 3 cases, which remained unclassifiable (4.92%). PAX-5 was expressed in 94% of CHL and 100% of DLBCL cases. LMP-1 was expressed in 52% of CHL and 25% of DLBCL cases. EMA was invariably expressed in all 4 cases of ALK+ALCL. It was expressed in 4/50 cases (8%) of CHL and in 2/4 cases (50%) of DLBCL. CD45 was expressed in all cases of ALCL and DLBCL but also in 3/50 cases (6%) of CHL. Conclusion: The differentiation between ALCL and CHL based on EMA and CD45 is not reliable. Utilization of PAX-5 in combination with other markers such as CD15 and LMP-1 is recommended. CD20 and PAX-5 are not too helpful in the differentiation of CHL and DLBCL, while CD15 and CD79a were found to be quite useful discriminative markers for this purpose.