Favorable Long-Term Outcomes after Daratumumab Discontinuation in AL Amyloidosis Patients Achieving Deep Responses
Authors: Chung Alfred , Kaufman Gregory P. , Sidana Surbhi , Iberri David , Eckhert Erik , Schrier Stanley , Lafayette Richard , Arai Sally , Witteles Ronald , Liedtke Michaela 
Published: November 2019

Daratumumab (DARA) is a CD38-targeted antibody FDA-approved for the treatment of multiple myeloma (MM) and its efficacy has recently been demonstrated in the treatment of AL amyloidosis. DARA is conventionally given indefinitely until evidence of disease progression or intolerance for the treatment of MM. In AL amyloidosis, the optimal duration of therapy is not known, and patients may be treated indefinitely on maintenance, extrapolating from MM data. However, the plasma cell burden observed in AL amyloidosis is often lower than in MM, and thus certain patients achieving deep responses may have durable responses with time-limited treatment. Outcomes for patients who are observed after DARA discontinuation are not known. We report the outcomes of patients at our institution who received time-limited DARA.
A retrospective analysis of AL amyloidosis patients treated at Stanford University from 2016 to 2019 with DARA monotherapy and dexamethasone for at least 2 months was performed, and patients who subsequently had DARA discontinued for reasons other than disease progression or lack of response were selected for the study. Hematologic responses were assessed by consensus guidelines. Duration on and off therapy were explored, along with time-to-next treatment or death (TTNT), defined as the time from DARA initiation to restarting/switching therapy or death. An exploratory analysis comparing TTNT between the study population and a control cohort who achieved hematologic CR and were maintained on DARA was conducted with the Kaplan-Meier method and log-rank testing.
67 patients received at least 2 months of DARA monotherapy and dexamethasone; among these, 15 patients discontinued therapy for reasons other than disease progression and were included. Median age was 66 years old and median lines of prior therapies was 4 (range: 1 - 6). Baseline difference between involved and uninvolved free light chains (dFLC) prior to DARA initiation was 2.6 mg/dL (range: 0 - 16.8 mg/dL). 10 of 15 patients had cardiac involvement with median NT-proBNP of 1982 pg/mL and 9 of 15 patients had renal involvement with median 24-hour proteinuria of 6.2 g and eGFR of 32 mL/min/1.73m2 at DARA initiation.
Median duration from starting to stopping DARA was 7.8 months (range: 2 - 21 months). Median duration from achieving best hematologic response to stopping DARA was 3 months (range: 0 - 17 months). Reasons for discontinuation included: patient preference (5), fatigue/body aches (4), infection (2), other active medical comorbidities (3), and lack of perceived further benefit (1). At DARA discontinuation, median dFLC was 0.1 mg/dL (range: 0 - 2.2 mg/dL) and there were 12 hematologic CR, 1 VGPR, 1 PR, and 1 not assessable for response.
Outcomes for all 15 patients are shown in Figure 1. The median treatment-free interval was 17.5 months (range: 5 - 34 months); estimated 2-year TTNT-free survival was 83% (95% CI: 61 - 100%). All 14 evaluable patients eventually achieved CR. 3 patients restarted DARA for rising dFLC, and all 3 patients demonstrated response to retreatment (2 achieving CR and 1 near PR with ongoing follow-up).
There were 2 deaths. One patient with severe baseline cardiac amyloidosis developed sudden rise in dFLC after treatment-free interval of 21 months; although he rapidly achieved hematologic CR on retreatment, he died of heart failure within 2 months of restarting DARA. The other patient developed therapy-related AML while off therapy and underwent allogenic stem cell transplant but died of leukemia (censored for AL amyloidosis outcomes at transplant).
There was no significant difference in the TTNT between the study group and a control group of 16 patients who achieved CR and were on continuous maintenance (Figure 2; p=0.807).
AL amyloidosis patients achieving deep responses with DARA can have favorable outcomes after treatment discontinuation, including a long treatment-free interval. Although our sample size is small, the outcomes of these patients appeared comparable to those achieving CR on continuous DARA maintenance, and patients were able to regain responses when retreatment was necessary. These results suggest that DARA may be safely discontinued in patents achieving deep hematologic responses, which has significant implications for quality of life and financial burden of treatment. Future studies evaluating time-limited versus continuous DARA maintenance after achievement of deep responses are warranted.

Disclosures
Kaufman: Janssen: Other: travel/lodging, Research Funding. Liedtke:Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Membership on an entity's Board of Directors or advisory committees, Research Funding; Prothena: Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; IQVIA/Jazz: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees, Research Funding; Genentech/Roche: Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees, Research Funding; Celator: Research Funding; Caelum: Membership on an entity's Board of Directors or advisory committees; BlueBirdBio: Research Funding; Amgen/Onyx: Consultancy, Honoraria, Research Funding; Agios: Research Funding; Adaptive: Membership on an entity's Board of Directors or advisory committees.

OffLabel Disclosure:
Daratumumab for treatment of AL amyloidosis