Molecular Biology Study of Primary Immuno-Privileged Lymphomas

Background: Primary immune-privileged lymphoma is a rare type of lymphoma and a new entity in 5^th WHO classification¹ that occurs in immune-privileged sites such as the central nervous system (CNS), testes, and vitreoretinal. Some other organs, such as the breast and skin, seem to share same clinical characteristics with them, and it is uncertain whether the classification will be expanded in the future. There are few studies on whether organ-specific extranodal lymphomas have the same molecular biological characteristics or immune environment. Also, there has been no breakthrough in the first-line treatment of DLBCL in recent years, but some new drugs have been found to have potential in specific genetic subtypes of lymphoma, such as the Bruton kinase (BTK) inhibitor ibrutinib, which has achieved a high ORR rate in patients with MCD subtypes.

Methods: This study included patients diagnosed with primary extranodal DLBCL involving the testes, CNS, and breast, from January 1, 2005 to June 30, 2023, at four centers. Clinical and imaging diagnoses were utilized to confirm the involvement of these organs, with histopathological diagnosis of primary extranodal DLBCL. Next, statistical methods were designed and implemented to compare with clinical and pathological characteristics and treatment efficacy. The follow-up deadline was January 15, 2024, with progression-free survival (PFS) as the observed primary outcome measures. Whole exome and whole genome sequencing were performed on samples with sufficient tumor tissue obtained from the clinical cohort, with systemic DLBCL treated during the same period included as controls. GATK, ANNOVAR, AcornCNV, and WisecondorX were used to identify somatic gene mutations and copy number variations, combined with BCL2 and BCL6-FISH for molecular subtyping.

Results:In this study, a total of 286 cases of DLBCL from four centers were included, including 192 cases of IP-LBCL (comprising 125 cases of primary testicular and 67 cases of primary central nervous system), and 94 cases of primary breast DLBCL. In terms of clinical characteristics, the median age of IP-LBCL was 61 years. Pathologically, all three subtypes were predominantly of non-germinal center origin (>70%), with a high proportion of BCL2/CMYC double-expressing patients (>30%), and double or triple-hit lymphomas accounting for less than 1%.In terms of molecular biology, this study conducted whole exome sequencing (WES) on 139 cases of DLBCL and whole genome sequencing (WGS) on 127 cases, including 62 cases of IP-LBCL (39 testicular and 23 central nervous system), 13 breast cases, and 64 DLBCL controls. The gene mutation spectrum of IP-LBCL (central nervous system and testicular) was similar to that of breast DLBCL. Compared with systemic DLBCL, MYD88, CD79B, PIM1, IGLL5, and OSBPL10 were common high-frequency recurring genes in all three subtypes.More data information could be obtained based on genome sequencing, and no single gene mutation or CNV was found to be significantly associated with prognosis. According to molecular subtyping based on self-developed optimized algorithms, IP-LBCL and breast DLBCL were mainly classified into MCD and BN2 subtypes. The prognosis of the BN2 subtype was relatively better, with 5-year PFS and OS rates of 61.00% and 81.45%, respectively. The combined 5-year PFS and OS rates for other subtypes were 54.81% and 73.94%, respectively, with no statistically significant differences.

Conclusion:IP-LBCL and breast DLBCL exhibit unique clinical and pathological features, with generally poor prognoses, especially for those originating CNS. Local recurrence and CNS relapse are the main patterns of relapse and progression, with currently limited clinical risk factors for prognosis assessment and guidance. IP-LBCL and breast DLBCL frequently exhibit mutations in genes such as MYD88, CD79B, PIM1, IGLL5, and OSBPL10, demonstrating a distinctive genomic profile related to BCR/TLR, PI3k/AKT, MHC antigen along with CDKN2A/2B loss, showcasing prevalent gentic subtype by MCD and BN2. This suggests that breast DLBCL may shares a high predisposition of "immune privilege" characteristics like to IP-LBCL. The molecular and biological features identified offer potential therapeutic targets for IP-LBCL and breast DLBCL.