S818 PRIMARY THERAPY AND SURVIVAL AMONG ADULT PATIENTS WITH NODULAR LYMPHOCYTE PREDOMINANT HODGKIN LYMPHOMA (NLPHL): A POPULATION‐BASED ANALYSIS IN THE NETHERLANDS, 1993–2016

Background: NLPHL is a rare, distinct and indolent subtype of Hodgkin lymphoma. At present, evidence to guide treatment decision‐making in NLPHL comes from a paucity of prospective and retrospective studies performed over the past decades. Population‐based studies—which are very scarce in NLPHL—can lend support to examine how treatment practices over time affected population‐level survival of patients with NLPHL Aims: The aim of this nationwide population‐based study was to assess trends in primary treatment and relative survival (RS) among NLPHL patients diagnosed in the Netherlands. Methods: We selected all adult (≥18 years) NLPHL patients diagnosed between 1993–2016 from the nationwide Netherlands Cancer Registry (NCR), with survival follow‐up through 2018. Data on primary therapy—i.e. no anti‐neoplastic therapy, radiotherapy (RT) alone, and therapy with a chemotherapeutic backbone—were available in the NCR. Patients were categorized into two calendar periods (1993–2002 and 2003–2016), sex, age categories (18–39, 40–59, and ≥60 years), and stage (I‐II and III‐IV). The time periods represent the pre‐ and post‐rituximab era, respectively. We calculated RS and excess mortality ratios up to ten years after diagnosis to estimate disease‐specific survival. Also, overall survival (OS) was calculated up to ten years after diagnosis to present outcomes according to primary therapy. Results: Our analytical cohort included 616 NLPHL patients (median age, 44 years; 74% males; 72% stage I‐II disease). The overall age‐standardized incidence rate increased from 1.0/1,000,000 to 2.2/1,000,000 person‐years between 1993–2002 and 2003–2016, respectively. This was a result of an increasing incidence in all three age groups across both sexes. There were no noteworthy trends in primary therapy over time. Overall, RT alone was the preferred treatment in stage I‐II disease (56%), whereas therapy with a chemotherapeutic backbone was preferred in stage III‐IV disease (77%). This was independent of age. Between 2007–2016, 40% and 57% of the chemotherapy recipients with stage I‐II and III‐IV disease received chemotherapy with rituximab ( P  = .095). The application of rituximab remained comparatively steady during this period. Rituximab use in earlier periods was not registered in the NCR. Ten‐year OS (95% confidence intervals) was 99% (96%–100%) and 80% (67%–88%) for patients with stage I‐II and III‐IV disease who received first‐line RT alone and first‐line therapy with a chemotherapeutic backbone, respectively. RS was generally excellent across the various subgroups studied (Fig 1). Interestingly, patients age 18–39 experienced no excess mortality (EM) as compared to the general population. Also, EM was comparatively low among patients age 40–59 and ≥60. The multivariable model demonstrated that EM was similar between the two calendar periods ( P  = 0.891) and sexes ( P  = .477), whereas there was a poor prognostic effect of older age ( P  = .005) and advanced stage ( P  < .001; Fig 1). Interestingly, EM was similar between patients age 40–59 and ≥60 ( P  = .674; Fig 1). Summary/Conclusion: In this large, nationwide population‐based study, survival among various subgroups of patients with NLPHL during a 23‐year period was largely comparable to the survival of the general population. Further, we noted no improved survival after the introduction of rituximab into the therapeutic arsenal of NLPHL since 2003. Future prospective studies in NLPHL are necessary to establish evidence‐based treatment recommendations that consider the delicate balance between efficacy, toxicity, and quality of life.