Risk Adjusted Management of Newly Diagnosed High and Intermediate FLIPI Follicular Lymphoma Using (90)Y Ibritumomab Tiuxetan

Background: Although the natural history of follicular lymphoma is indolent with a median overall survival of about 12-15 years, the disease is heterogeneous. The 5 and 10 year overall survival (OS) of low, intermediate and high risk FLIPI is 91%, 78% and 53% and 71%, 51% and 36% using standard rituximab-based treatment. 5-year progression-free survival (PFS) is 80%, 70% and 48% respectively. Methods: Based upon this we conducted an investigator-initiated single-centre Phase II trial of intensified therapy with CHOP-R followed by (90)Y ibritumomab tiuxetan consolidation and 24 months of rituximab maintenance as treatment for patients with intermediate and high-risk newly diagnosed symptomatic follicular lymphoma. 33 patients were enrolled. Results: The addition of (90)Y ibritumomab tiuxetan was well tolerated but resulted in asymptomatic grade 3 or 4 thrombocytopenia and neutropenia in11-36% and 10-24% of patients between weeks 2-8 post (90) Y. After 9 years of follow-up (median follow-up 61 months) the 0S for intermediate and high risk FLIPI was 95% and 78%. The 5 year PFS was 79% and 64% for intermediate and high risk FLIPI, respectively. Responses at three months post consolidation were as follows: 3/33 (9%) achieved CR, 25/33(76%), achieved CRU, 1/33(3%) had PR, and 1/33(3%) had PD. Three patients did not receive (90)Y ibritumomab tiuxetan due to disease progression 2/33(6%), or death 1/33(3%). Of 19 patients who had a molecular marker for their lymphoma, 18 (95%) achieved molecular remissions in peripheral blood with CHOP-R therapy. Nine (47%) of these patients have been recently assessed for MRD and remain in molecular remission. The therapy resulted in decreased levels of IgG, IgM and IgA below the lower normal level in 33%, 40% and 23% of patients respectively post therapy. These levels did not recover in most of these patients. B cells were depleted to undetectable levels during therapy including rituximab maintenance. In 18 evaluable patients only 11 recovered normal B cell counts post maintenance rituximab. There was no correlation between normal B-cell recovery and Ig levels. Many patients with low or no B cell counts had normal IgG levels, whereas some patients who regained normal B cell counts were still unable to reach normal Ig levels. No patient developed human anti-mouse antibody. Immunity to measles, mumps, or rubella was retained post therapy. Patients did not have significant infections or opportunistic infections (although 2 developed Grade 1 shingles post (90)Y ibritumomab tiuxetan) and none required IVIG. Conclusions: We conclude that this intensified regimen is highly active in cyto-reducing lymphoma in high and intermediate risk FLIPI follicular lymphoma patients. The toxicity is tolerable although a significant percentage of patients will end up with persistent asymptomatic reductions in B cells and serum Ig. Only randomized trials will determine whether this regimen enhances outcome over standard of care in this higher risk follicular lymphoma population. References: 1.Examination of the follicular lymphoma international prognostic index (FLIPI) in the National LymphoCare study (NLCS): a prospective US patient cohort treated predominantly in community practices. Nooka AK, Nabhan C, Zhou X, Taylor MD, Byrtek M, Miller TP, Friedberg JW, Zelenetz AD, Link BK, Cerhan JR, Dillon H, Sinha R, Shenoy PJ, Levy D, Dawson K, Hirata JH, Flowers CR. Ann Oncol. 2013 Feb;24(2):441-8. doi: 10.1093/annonc/mds429. Epub 2012 Oct 5 2.Validation, revision and extension of the Follicular Lymphoma International Prognostic Index (FLIPI) in a population-based setting. van de Schans SA, Steyerberg EW, Nijziel MR, Creemers GJ, Janssen-Heijnen ML, van Spronsen DJ. Ann Oncol. 2009 Oct;20(10):1697-702. doi: 10.1093/annonc/mdp053. Epub 2009 Jun 23. PMID: 19549712 Disclosures Buckstein: Novartis: Honoraria; Celgene: Honoraria, Research Funding.