Abstract Introduction: Although the spleen is involved in about a third of patients with Diffuse Large B-cell Lymphoma (DLBCL), stage I splenic DLBCL is rare and there is little data to guide management. Potential treatment modalities include combinations of splenectomy, radiation and immuno-chemotherapy, but there is no consensus on the optimal approach. Using multiple publically available and propriety databases, we sought to further define the prognosis and outcomes for stage I splenic DLBCL. Methods: We utilized the Surveillance Epidemiology and End Results (SEER) 18 registry to identify patients with stage I splenic DLBCL diagnosed during the years 1973-2013. Appropriate cases were identified using a combination of International Classification of Diseases for Oncology, 3rd edition code DLBCL (9680/3) and location code for spleen (C42.2). These patients were divided into two cohorts based on the year of diagnosis (1983-2005; 2006-2013) as rituximab (R) was approved by the FDA in 2006 for use in the first line treatment of DLBCL. Patient characteristics and survival outcomes were analyzed by GraphPad Prism 6 and Microsoft Excel. Disease specific survival (DSS) and Overall survival (OS) comparisons were made using the Gehan-Breslow-Wilcoxon test. All p-values were 2-sided and results ≤0.05 were considered significant. We queried the Mitelman Database of Chromosome Aberrations and Gene Fusions in Cancer to identify patients with stage I splenic lymphoma during the years 1973-2013. We also searched the Caris Life Sciences database for patients profiled by Caris Molecular Intelligence using the keywords "splenic lymphoma " in the clinical history and diagnosis fields for cases of stage I splenic DLBCL from 2007-2015. All database searches were conducted with IRB approval. Results: 107,550 patients with known stage and histologically confirmed DLBCL were identified within the SEER database. 30,455 patients had stage I disease with 470 of them diagnosed as stage I splenic DLBCL. The mean age was 66 years (range, 17-93 years) and the majority were Caucasian (89%). There was equal distribution of patients in the pre-rituximab (pre-R) era and post rituximab (R) era (53% vs 47%). 42% (470/1116) of splenic DLBCL were diagnosed as stage I compared to 28% (29,985/106,434) of all other types of DLBCL (p<0.01). Stage I splenic DLBCL treated in the R-era has better OS than all other stage I DLBCLs treated during the same period (HR = 0.62, 95% CI 0.53-0.86, p<0.01) The rate of splenectomy was lower after the approval of rituximab (82% in pre-R vs 72% in R era, p=0.03). Splenectomy was associated with an improvement in DSS (HR = 0.57, 0.28 - 0.96, p=0.04), but when stratified by pre-R and R era, improved DSS with splenectomy was only seen in the pre-R (HR = 0.51, 0.17-1.08, p =0.04), but not in the R-era (HR =0.62, 0.25 - 1.38 p=0.53). OS advantage with splenectomy was also seen only in the pre-R era (HR = 0.66, 0.32 - 1.14, 106m vs 137m, p=0.03) but splenectomy had no impact on OS in the R-era (HR = 0.74, 0.37 - 1.43, p=0.45). There was a trend toward improved OS with the introduction of rituximab (HR = 0.75, 0.48 - 1.14, p=0.054). There was no difference in the utilization of radiation between these cohorts (6% in pre-R vs 3% in R era, p=0.13). Our search of the Mitelman database found 1413 patients with DLBCL, but none of them had stage I splenic DLBCL. We also identified 20 patients with Non-Hodgkin lymphoma profiled by Caris Life Sciences, of which only one had primary splenic DLBCL. This patient was a 35 year old male who on immunohistochemistry was found to be positive for MGMT, MRP1, PTEN, TOP2A, TOPO1, and TS. Conclusion: The utilization of splenectomy for stage I splenic DLBCL has decreased with the introduction of rituximab without compromise of outcomes. Radiation is rarely used and does not appear to influence outcomes. Splenic DLBCL is more likely to present as stage I disease compared to other types of DLBCLs and Stage I splenic DLBCL appears to have a favorable prognosis relative to other stage I DLBCLs. Alternative databases added little to the understanding of the biology of stage I splenic DLBCL. Disclosures No relevant conflicts of interest to declare.

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