Abstract 3373: Circulating tumour DNA mutations correlate with relapse in a phase II trial of bortezomib-primary refractory multiple myeloma patients receiving salvage therapy
Authors: Mithraprabhu Sridurga , Reynolds John , Kalff Anna , Bergin Krystal , Turner Rose , Quach Hang , Horvath Noemia , Kerridge Ian , Yuen Flora , Choi Kawa , Ramachandran Malarmathy , George Ashley , Khong Tiffany , Durie Brian , Spencer Andrew 
Published: June 2022

Abstract
Background: Multiple myeloma (MM), an incurable plasma cell malignancy, has a relative 5-year overall survival (OS) of 48.5% for newly diagnosed patients. Prospective real-world data reveals that 23% of transplant eligible MM patients relapse within 12 months of starting first-line bortezomib based therapy with a median OS of only 16.8 months (high-risk - HR). Genomic studies for these HR patients could inform rational secondary therapeutic options and prolong survival. Bone marrow (BM) genomic analysis in MM has methodological and conceptual shortcomings owing to the spatially and genomically heterogeneous nature of MM that can be largely overcome with circulating tumour DNA (ctDNA) analysis.
Objective: To determine whether ctDNA analysis can define the mutational spectrum of patients with HR MM.
Design: Phase II, multicentre single arm study of carfilzomib-thalidomide-dexamethasone (KTd) in 50 transplant-eligible newly diagnosed MM patients from September 2016 to April 2018 (Australasian Leukaemia and Lymphoma Group (ALLG) - MM17 trial) who were refractory (REF) to or demonstrated a suboptimal response (SOR) to bortezomib-based induction therapy. A total of 186 peripheral blood plasma and BM samples were obtained at baseline, at Cycle 3 day 1 (C3D1), end of the study (EOS) and/or at relapse. Somatic variants were identified with an ultra-sensitive targeted amplicon sequencing (TAS) assay incorporating 22-genes known to be mutated in MM. The mutational spectrum was correlated with progression-free survival (PFS) and OS.
Results: TAS of 31 BM samples and 48 ctDNA samples revealed that in BM, KRAS mutations were detected in 42% of patients followed by ATR in 29% while in ctDNA, ATR mutations were prominent (36%), followed by FGFR3 and ATM (27% and 26.8%). We compared the ctDNA mutational spectrum at baseline between non-relapse and relapse patients on KTd and identified a significant difference in the proportion of patients with specific mutations - RAS/RAF: 3% vs 25%; ATM/ATR/TP53: 17% vs 41%, respectively (p&lt;0.0001). Patients with RAS/RAF and/or ATM/ATR/TP53 ctDNA mutations at baseline had significantly shorter PFS and OS (p=0.003 and p=0.02, respectively). Comparative ctDNA TAS for baseline, C3D1, EOS/relapse, demonstrated that in 87.5% of patients, one or more dominant mutations driving relapse in KTd were already present prior to starting salvage therapy. We also performed ctDNA analysis to compare patients who were REF or SOR to front-line therapy and identified 62% of REF patients had RAS/RAF or ATM/ATR/TP53 mutation compared to 35% of SOR patients (p=0.0002, Fisher’s exact test).
Conclusions: Our results demonstrate that RAS/RAF and ATM/ATR/TP53 mutations in ctDNA are prognostic biomarkers of outcome to secondary salvage therapy in HR patients thus enabling design of targeted therapeutic approaches to improve survival.
Citation Format: Sridurga Mithraprabhu, John Reynolds, Anna Kalff, Krystal Bergin, Rose Turner, Hang Quach, Noemia Horvath, Ian Kerridge, Flora Yuen, Kawa Choi, Malarmathy Ramachandran, Ashley George, Tiffany Khong, Brian Durie, Andrew Spencer. Circulating tumour DNA mutations correlate with relapse in a phase II trial of bortezomib-primary refractory multiple myeloma patients receiving salvage therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3373.