Diagnostic utility of programmed cell death ligand 1 (clone SP142) in mediastinal composite lymphoma: A report of two cases

Hodgkin Lymphoma: Biology and Differential Diagnostic Problem

Hodgkin lymphomas (HLs) are lymphoid neoplasms that are morphologically defined as being composed of dysplastic cells, namely, Hodgkin and Reed–Sternberg cells, in a reactive inflammatory background. The biological nature of HLs has long been unclear; however, our understanding of HL-related genetics and tumor microenvironment interactions is rapidly expanding. For example, cell surface overexpression of programmed cell death 1 ligand 1 (CD274/PD-L1) is now considered a defining feature of an HL subset, and targeting such immune checkpoint molecules is a promising therapeutic option. Still, HLs comprise multiple disease subtypes, and some HL features may overlap with its morphological mimics, posing challenging diagnostic and therapeutic problems. In this review, we summarize the recent advances in understanding the biology of HLs, and discuss approaches to differentiating HL and its mimics.

Diagnostic utility of programmed cell death ligand 1 (clone SP142) immunohistochemistry for malignant lymphoma and lymphoproliferative disorders: A brief review

The programmed cell death 1 (PD1)/PD1 ligand (PD-L1) axis plays an important role in tumor cell escape from immune control and has been most extensively investigated for therapeutic purposes. However, PD-L1 immunohistochemistry is still not used widely for diagnosis. We review the diagnostic utility of PD-L1 (by clone SP142) immunohistochemistry in large-cell lymphomas, mainly consisting of classic Hodgkin lymphoma (CHL) and diffuse large B-cell lymphoma (DLBCL). Neoplastic PD-L1 (nPD-L1) expression on Hodgkin and Reed-Sternberg cells is well-established among prototypic CHL. Of note, EBV+ CHL often poses a challenge for differential diagnosis from peripheral T-cell lymphoma with EBV+ non-malignant large B-cells; their distinction is based on the lack of PD-L1 expression on large B-cells in the latter. The nPD-L1 expression further provides a good diagnostic consensus for CHL with primary extranodal disease conceivably characterized by a combined pathogenesis of immune escape of tumor cells and immunodeficiency. Compared with CHL, the nPD-L1 expression rate is much lower in DLBCL, highlighting some specific subgroups of intravascular large B-cell lymphoma, primary mediastinal large B-cell lymphoma, and EBV+ DLBCL. They consist of nPD-L1-positive and -negative subgroups, but their clinicopathological significance remains to be elucidated. Microenvironmental PD-L1 positivity on immune cells may be associated with a favorable prognosis in extranodal DLBCL. PD-L1 (by SP142) immunohistochemistry has helped us to understand the immune biology of lymphoid neoplasms possibly related by immune escape and/or immunodeficiency. However, knowledge of these issues remains limited and should be clarified for diagnostic consensus in the future.

Age-related EBV-associated B-cell lymphoproliferative disorders and other EBV + lymphoproliferative diseases: New insights into immune escape and immunodeficiency through staining with anti-PD-L1 antibody clone SP142

Epstein-Barr virus (EBV) is prevalent among healthy individuals, and is implicated in numerous reactive and neoplastic processes in the immune system. The authors originally identified a series of senile or age-related EBV-associated B-cell lymphoproliferative disorders (LPD) bearing a resemblance to immunodeficiency-associated ones. These LPDs may be associated with immune senescence and are now incorporated into the revised 4th edition of 2017 WHO lymphoma classification as EBV-positive (EBV+) diffuse large B-cell lymphoma (DLBCL), not otherwise specified (NOS). These EBV+ B-cells often have a Hodgkin/Reed-Sternberg (HRS)-like appearance and are shared beyond the diagnostic categories of mature B-cell neoplasms, mature T-cell neoplasms, classic Hodgkin lymphoma, and immunodeficiency-associated LPD. In addition, peculiar new diseases, such as EBV+ mucocutaneous ulcer and EBV+ DLBCL affecting the young, were recognized. On the other hand, lymphoma classification is now evolving in accord with deeper understanding of the biology of programmed death ligand 1 (PD-L1). Assessing PD-L1 positivity by staining with the anti-PD-L1 monoclonal antibody SP142 provides new insight by discriminating between immune evasion and senescence or immunodeficiency. The aim of the present review is to briefly summarize the diagnostic use of immunostaining with SP142 in malignant lymphomas and/or LPDs that feature tumor and nonmalignant large B-cells harboring EBV.