Abstract 2954: Immunomodulator maintenance post autologous stem cell transplant predicts better outcome in multiple myeloma patients with clonal hematopoiesis of indeterminate potential

Introduction: Multiple Myeloma (MM) is a clonal plasma cell malignancy, accounting for 10% of all hematological malignancies. Genetic analyses of large populations revealed that blood-specific somatic mutations in hematopoietic stem cells (HSCs) are commonly acquired during aging, a new entity labeled: clonal hematopoiesis of indeterminate potential (CHIP). We sought to determine the role of CHIP on survival of MM patients, specifically those receiving immunomodulators (IMiDs) maintenance (Lenalidomide or Thalidomide) post autologous stem cell transplant (ASCT). Methods: We tested cryopreserved HSCs of 629 MM patients who underwent ASCT between 2003 and 2011 at the Dana-Farber Cancer Institute. We used a target bait panel of 224 genes and performed deep-targeted sequencing at 978x coverage and ultra-low pass whole-genome sequencing at 0.1x to account for tumor contamination. Sequencing data was analyzed using ichorCNA, MuTect, and Strelka and mutation annotations were based on reported mutations in the literature and databases (ClinVar, COSMIC, cBioPortal, TCGA, and ExAC). Results: Our cohort had a median age of 58 years [24-83] at time of ASCT and median follow up post ASCT of 8 years [0.1-14.5]. 24% of patients had CHIP at time of ASCT, which is statistically similar to the 30% reported in non-Hodgkin9s lymphoma (NHL), (Gibson et. al, JCO, 2017). The most commonly detected mutated genes were DNMT3A, TET2, TP53 and ASXL1. Acquiring mutations positively correlated with age (p=0.004). In contrast to NHL, PPM1D was not significantly mutated in MM (40% vs. 3.3%). 27 patients (4.3%) developed a second hematological malignancy at median of 4 years [1-10] post ASCT, of which 10 had CHIP. 22% received at least 3 years [0.06-12.8] of IMiD maintenance. Among those who did not receive IMiD maintenance, CHIP was associated with worse progression free survival (PFS) (p=0.047) where PFS at 3 years post ASCT was 31% (95%CI: 25-38) for those without CHIP vs. 15% with CHIP (95%CI: 7-25). In patients with IMiD maintenance, CHIP had no effect on PFS or overall survival (OS) (p=0.9). In patients with CHIP, receiving IMiD was associated with a better OS and PFS below the age of 58 and better PFS only in those above 58. In the overall cohort, CHIP was not associated with more adverse outcomes, which could be attributed to low OS and PFS in MM or the use of IMiD in 56% of this cohort. IMiD maintenance was associated with better OS (p Conclusion: CHIP is a common entity among MM patients that predicts a worse PFS in those who do not receive IMiD maintenance therapy post ASCT. The use of IMiDs abrogated the deleterious effect imposed by CHIP in this cohort. Larger cohorts with longer follow up are needed, especially in the era of novel agents and long-term use of Lenalidomide maintenance. Citation Format: Tarek H. Mouhieddine, Jihye Park, Robert Redd, Christopher J. Gibson, Salomon Manier, Amin Nassar, Kalvis Hornburg, Marzia Capelletti, Daisy Huynh, Romanos Sklavenitits Pistofidis, Mark W. Bustoros, Saud H. AlDubayan, Brendan Reardon, Cody J. Boehner, Henry Dumke, Chia-Jen Lui, Darlys Schott, Eliezer M. Van Allen, Robert L. Schlossman, Nikhil C. Munshi, Kenneth C. Anderson, David P. Steensma, Jacob P. Laubach, Paul G. Richardson, Jerome Ritz, Benjamin L. Ebert, Robert J. Soiffer, Donna Neuberg, Irene M. Ghobrial. Immunomodulator maintenance post autologous stem cell transplant predicts better outcome in multiple myeloma patients with clonal hematopoiesis of indeterminate potential [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2954.