Background: Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous disease and in 30-40% cases can present or relapse at extranodal sites. Primary extranodal DLBCL (EN-DLBCL) is defined as disease presenting as clinically dominant extranodal masses with no or only minor nodal disease. EN-DLBCL is predominantly of the activated B-cell (ABC) and less commonly of germinal center B-cell (GCB) like DLBCL subtype. We aimed to identify genetic characteristics of EN GCB-DLBCL to gain insights into extranodal tropism and aggressive clinical behavior. Methods: Patient data was collected via retrospective chart review. Inclusion criteria consisted of pathologically confirmed diagnosis of GCB-DLBCL by the Hans algorithm, extra-nodal involvement at diagnosis or relapse, and availability of next-generation sequencing (NGS). Overall (OS) and progression-free survival (PFS) were analyzed using the Kaplan-Meier method. Results: Fifteen patients were identified. The median age at diagnosis was 64 years (range 33-89) and majority were men (62.5%). Two patients had purely nodal disease at presentation that relapsed at EN sites, while the remainder (13/15) had predominantly EN disease. EN sites included central nervous system [CNS] (n = 5), bone marrow (n = 4), epidural (n=4), bone (2), paranasal sinus (1), testes (1), stomach (n = 2), lung/pleura (n=2), and liver (n=3). Nine patients had disease in multiple EN sites. All patients had advanced stage disease and median IPI score was 3 (range 3-4). On FISH/cytogenetic analysis, two patients had MYC and four patients had BCL2 rearrangements. Copy gains in BCL6, BCL2 and MYC were seen in 2, 1 and 4 patients respectively. No patients had evidence of MYC and BCL2 and/or BCL6 rearrangements (double hit). TP53 deletion was seen in 1 patient. On NGS, prominent gene mutations identified were KMTD2 (8/15, 53%), TP53 (5/15, 33%), TNFRSF14 (4/15, 27%), and evidence of aneuploidy with abnormalities in chromosome 12 (5/15, 33%), chromosome 6 (4/15, 27%), and chromosome 8 (4/15, 27%), including both losses and gains of function. Notably, MYD88 (3/15, 20%), CARD11 (2/15, 13%), and IRF4 (2/15, 15%) mutations, representative of BCR/TLR4 pathway activation and NF-kB signaling were seen at initial presentation. All patients were treated with chemo-immunotherapies incorporating CNS prophylaxis and 2 patients received salvage CAR T-cell therapy. Median OS was 1.3 years and median PFS was 11.3 months. Nine patients (63%) progressed, with CNS relapses in 5 and of these, 7 patients died. Conclusions: This study shows that EN GCB-DLBCL is molecularly similar to EN ABC-DLBCL; specifically, activation of NF-kB pathway signaling through gene mutations involving the MCD (MyD88/CD79B) cluster is prominent, and this potentially enables extranodal tropism. The complex karyotype and TP53 mutations may contribute to chemoresistance and aggressive disease biology. Our results provide valuable molecular information and can aid in personalizing treatment strategies for this uncommon, aggressive DLBCL subset.

Citation Format: Akshat Patel, Brian Lue, Kiran A Kumar, Farrukh T Awan, Jeffrey Gagan, Weina Chen, Praveen Ramakrishnan Geethakumari. Clinico-pathologic and molecular characteristics of primary extranodal germinal-center B-cell like diffuse large B-cell lymphoma (EN GCB-DLBCL) [abstract]. In: Proceedings of the Third AACR International Meeting: Advances in Malignant Lymphoma: Maximizing the Basic-Translational Interface for Clinical Application; 2022 Jun 23-26; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2022;3(5_Suppl):Abstract nr A15.