SOHO State of the Art Updates and Next Questions: Prophylaxis and Management of Secondary CNS Lymphoma

Primary large B-cell lymphomas of immune-privileged sites

ABSTRACT

Diffuse large B-cell lymphoma (DLBCL) encompasses a diverse spectrum of aggressive B-cell lymphomas with remarkable genetic heterogeneity and myriad clinical presentations. Multiplatform genomic analyses of DLBCL have identified oncogenic drivers within genetic subtypes that allow for pathologic subclassification of tumors into discrete entities with shared immunophenotypic, genetic, and clinical features. Robust classification of lymphoid tumors establishes a foundation for precision medicine and enables the identification of novel therapeutic vulnerabilities within biologically homogeneous entities. Most cases of DLBCL involving the central nervous system (CNS), vitreous, and testis exhibit immunophenotypic features suggesting an activated B-cell (ABC) origin. Shared molecular features include frequent comutations of MYD88 (L265P) and CD79B and frequent genetic alterations promoting immune evasion, which are hallmarks of the MCD/C5/MYD88 genetic subtype of DLBCL. Clinically, these lymphomas primarily arise within anatomic sanctuary sites and have a predilection for remaining confined to extranodal sites and strong CNS tropism. Given the shared clinical and molecular features, the umbrella term primary large B-cell lymphoma of immune-privileged sites (IP-LBCL) was proposed. Other extranodal DLBCL involving the breast, adrenal glands, and skin are often ABC DLBCL but are more heterogeneous in their genomic profile and involve anatomic sites that are not considered immune privileged. In this review, we describe the overlapping clinical, pathologic, and molecular features of IP-LBCL and highlight important considerations for diagnosis, staging, and treatment. We also discuss potential therapeutic vulnerabilities of IP-LBCL including sensitivity to inhibitors of Bruton tyrosine kinase, immunomodulatory agents, and immunotherapy.

Bruton's tyrosine kinase (BTK) inhibitors for the treatment of primary central nervous system lymphoma (PCNSL): current progress and latest advances

The incidence of primary central nervous system lymphoma (PCNSL) has steadily increased, particularly in elderly patients. Although highly responsive to first-line chemotherapy and radiotherapy, approximately 50% of patients relapse or become refractory within 1 year. Prognosis following relapse is dismal and no standard salvage therapy exists. Bruton's tyrosine kinase (BTK), a key regulator of the B-cell receptor (BCR) pathway, has emerged as a promising therapeutic target. The first BTK inhibitor ibrutinib has been evaluated in the relapsed/refractory PCNSL setting, with overall response rates of 51.9%-89.0% and median progression-free survival of 4.6-4.8 months. However, ibrutinib inhibits several kinases in addition to BTK, leading to off-target effects. Second-generation BTK inhibitors have since been developed, which afford greater selectivity for BTK and fewer off-target effects. We review current practices in the diagnosis and evaluation of PCNSL, as well as clinical trials of BTK inhibitors in PCNSL and future developments in PCNSL treatment.