HIGH RESPONSES RATES WITH SINGLE AGENT BELANTAMAB MAFODOTIN IN RELAPSED SYSTEMIC AL AMYLOIDOSIS

ABSTRACT

Background: Systemic AL amyloidosis is an incurable relapsing plasma cell disorder. Despite therapeutic advances, there are no approved treatments for relapse disease. Treatment is often challenging due to underlying organ dysfunction. Belantamab mafodotin is an antibody-drug conjugate targeting B-cell maturation antigen with approval for relapsed refractory myeloma. In multiply pre-treated myeloma, the DREAMM-2 phase II trial showed an overall response rate of 32% for those with 2.5 mg/kg dose administered every three weeks with 2/3rd patients reporting keratopathy. A small case series of 6 patients with relapsed AL amyloidosis (Zhang et al , ASH 2021) was recently reported and a phase 2 trial is recruiting for patients with refractory amyloidosis (NCT04617925). Aims: We report our initial results using Belantamab monotherapy for the treatment of patients with AL amyloidosis with relapsed disease. Methods: Data for consecutive patients who were administered Belantamab at a specialist referral centre, National Amyloidosis Centre, University College London, was analysed. Results: Eleven patients were included 8 male, 3 female. Median age at Belantamab initiation was 65 (range 42-74) years. Eight patients had λ AL-type and three κ AL-type. At diagnosis, median involved free light-chain concentration was 534 (range 73-7181) mg/l. A median of two organs involved at baseline (range 1-3) 4 had cardiac involvement (half Mayo stage 2;half Mayo stage 3a) and 8 had renal involvement. The median prior lines of therapy was 3 (range 2-5) with all exposed to prior immunomodulatory drugs, proteasome inhibitors and 73% to anti-CD38 antibody treatments. Thirty-six percent had relapsed after melphalan-conditioned autologous stem cell transplantation. A median of 3 cycles of belantamab were delivered (range 1-8). The most frequent adverse event was ocular toxicity which was experienced in 8 patients (grade 1-3), necessitating dose modification of the three-weekly schedule. One patient developed transient grade 1 dyspnoea and liver dysfunction. No patients developed cytopenias, unlike previous reports (Zhang et al , 2021), nor infections beyond COVID (2 patients mild with no hospital admissions). The majority of the cohort required dose reduction either at initiation (patient 4, due to end stage renal failure;patient 11, post-renal transplant) or during therapy (n=5;three to 1.9mg/kg, two to 1.25mg/kg) due to ocular toxicity. Only one patient remained on the standard dose of 2.5mg/kg for >3 cycles. Ocular toxicity improved after treatment interruption (drug intervals 4-6 weeks) and no patients required complete treatment cessation. One patient is too early to assess response. Haematological responses (PR or better) were seen in 7 patients with 3 complete responses and two very good partial responses (VGPR) which are ongoing. Both renal patients (patients 4 and 11) commenced a dose of 1.25mg/kg and sustained a VGPR with no additional toxicity. Patient 3 had a 42% reduction in sFLC after two doses but then a prolonged gap due to keratopathy and has lost the response. There were no cardiac or renal toxicities observed. Summary/Conclusion: Belantamab mafodotin demonstrates significant activity in patients with heavily pre-treated AL amyloidosis with 70% achieving a ≥PR. Apart from keratopathy requiring dose modification, no other substantial toxicity was observed. Two patients with renal impairment (stage V CKD and ESRD) and one patient post-renal transplant tolerated treatment with no additional toxicity. Belantamab mafodotin shows promise in treatment of relapsed AL and needs further prospective trials.