Molecular Subtypes of Splenic Marginal Zone Lymphoma (SMZL) Are Associated with Distinct Pathogenic Mechanisms and Outcomes – Interim Analysis of the IELSG46 Study

Introduction. The majority of SMZLs display an indolent course, however the disease is still incurable and a significant proportion of patients (~25-30%) experience poor outcomes surviving 5 years, and for whom tumor material collected before initiation of medical therapy was available. Mutation analysis was performed by CAPP-seq targeted deep next generation sequencing of tumor genomic DNA. A stringent bioinformatic pipeline was applied to suppress the background noise allowing to call variants with a sensitivity of 5x10-2 in FFPE derived DNA. Copy number variations(CNVs) were identified by using the sequencing reads-based GATK4-CNV algorithm. IGHVrearrangements were obtained by using LymphoTrack® IGH FR1 Assay Panel kit. Molecular clusters were identified by an iterative algorithm that maximizes genetic distinctiveness of subgroups by reassigning patients between clusters that are created a priori based on the co-occurrence of genetic lesions. Relative survival, defined as the ratio between actuarial survival observed in the SMZL cohort and expected survival of the general population matched to patients by geographical origin, sex, age and calendar year of diagnosis, was calculated using the Ederer II method. Results. The analysis included 303 patients with a SMZL diagnosis confirmed on spleen histology. The sample size allowed to identify 30% differences in survival for molecular subgroups comprising at least 5% of cases with a statistical power between 80-100%. Median follow-up was 9.2 years. At 10 years, 85% of patients were alive, consistent with the known indolent behavior of this lymphoma. Genes recurrently affected by non-synonymous somatic mutations in >10% of SMZL included KLF2(24%), NOTCH2 (19%), KMT2D (15%), TNFAIP3(13%), EP300and TP53 (10%). Deletion 7q was documented in 25% of cases and IGHV1-2*04 usage in 32%. By cluster analysis, three major molecular subgroups were identified, each of them characterized by a NOTCH pathway mutated gene (Fig. 1A). The first cluster was defined by NOTCH2 and/or KLF2mutations and was enriched in TNFAIP3mutations and IGHV1-2*04 gene usage (Fig. 1A). The second cluster was defined by SPEN mutations, and was enriched in KMT2D and other epigenetic gene mutations (Fig. 1A). The third cluster was enriched in NOTCH1 mutations (Fig. 1A). By relative survivalanalysis, the NOTCH2/ KLF2cluster showed a lower survival compared to the matched general population, indicating a significant impact of the disease on patients9 expected survival (Fig. 1B). Conclusions. The large sample size and inclusion of SMZL confirmed by spleen histopathology review allowed for precise estimation of the prevalence of KLF2and NOTCH2 mutations in this lymphoma. Three molecular clusters were identified in SMZL, each of them containing a NOTCH pathway gene, supporting the relevance of NOTCH signaling in the pathogenesis of SMZL. Patients belonging to the NOTCH2/ KLF2cluster had a lower relative survivalcompared to the matched general population. Disclosures Traverse-Glehen:Astra Zeneca: Other: Travel; Takeda: Research Funding. Gomes da Silva:Roche: Other: Institution9s payment for consultancy, Travelling support; BMS: Consultancy, Membership on an entity9s Board of Directors or advisory committees, Other: lecture fees; Celgene: Other: Travelling support; Janssen: Consultancy, Membership on an entity9s Board of Directors or advisory committees, Other: lecture fees, Institution9s payment for consultancy, Travelling support; Abbvie: Consultancy, Membership on an entity9s Board of Directors or advisory committees, Other: lecture fees; Gilead Sciences: Consultancy, Membership on an entity9s Board of Directors or advisory committees, Other: lecture fees, Research Funding. Ladetto:Celgene: Honoraria; Jannsen: Honoraria; Acerta: Honoraria; Abbvie: Honoraria; Sandoz: Honoraria; Roche: Honoraria. Rambaldi:Pfizer: Consultancy; Novartis: Consultancy; Omeros: Consultancy; Italfarmaco: Consultancy; Amgen Inc.: Consultancy; Roche: Consultancy; Celgene: Consultancy. Vitolo:Takeda: Speakers Bureau; Sandoz: Speakers Bureau; Gilead: Speakers Bureau; Janssen: Membership on an entity9s Board of Directors or advisory committees, Speakers Bureau; Roche: Membership on an entity9s Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Membership on an entity9s Board of Directors or advisory committees, Research Funding, Speakers Bureau. Zinzani:MSD: Honoraria, Speakers Bureau; Gilead: Honoraria, Membership on an entity9s Board of Directors or advisory committees, Speakers Bureau; SERVIER: Honoraria, Membership on an entity9s Board of Directors or advisory committees, Speakers Bureau; TG Pharmaceuticals: Honoraria, Membership on an entity9s Board of Directors or advisory committees; Bayer: Membership on an entity9s Board of Directors or advisory committees; PFIZER: Honoraria, Membership on an entity9s Board of Directors or advisory committees; Merck: Honoraria, Membership on an entity9s Board of Directors or advisory committees; Janssen: Honoraria, Speakers Bureau; Bayer: Membership on an entity9s Board of Directors or advisory committees; TG Pharmaceuticals: Honoraria, Membership on an entity9s Board of Directors or advisory committees; BMS: Honoraria, Membership on an entity9s Board of Directors or advisory committees, Speakers Bureau; Celltrion: Honoraria, Membership on an entity9s Board of Directors or advisory committees, Speakers Bureau; Takeda: Membership on an entity9s Board of Directors or advisory committees; PFIZER: Honoraria, Membership on an entity9s Board of Directors or advisory committees; Verastem: Honoraria, Membership on an entity9s Board of Directors or advisory committees, Speakers Bureau; Celgene: Honoraria, Membership on an entity9s Board of Directors or advisory committees, Speakers Bureau; Merck: Honoraria, Membership on an entity9s Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity9s Board of Directors or advisory committees; AstraZeneca: Speakers Bureau. Gaidano:Roche: Consultancy, Honoraria; Gilead: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Morphosys: Honoraria; Amgen: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. Salles:Servier: Honoraria; Abbvie: Honoraria; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria; Amgen: Honoraria; BMS: Honoraria, Other: Advisory Board; Celgene: Honoraria, Other: Advisory Board, Research Funding; Acerta: Honoraria; Janssen: Honoraria, Other: Advisory Board; Merck: Honoraria; Pfizer: Honoraria; Morphosys: Honoraria; Gilead: Honoraria, Other: Advisory Board; Epizyme: Honoraria; Servier: Honoraria, Other: Advisory Board; Takeda: Honoraria. Zucca:Celltrion: Consultancy; AstraZeneca: Consultancy.