Hematologic Responses and Cardiac Organ Improvement in Patients with Heavily Pretreated Cardiac Immunoglobulin Light Chain (AL) Amyloidosis Receiving Daratumumab

Introduction: In immunoglobulin light chain (AL) amyloidosis, cardiac involvement is the primary cause of premature death. Light chain suppression, with therapies targeting the underlying plasma cell clone producing amyloidogenic free light chains, has been difficult to achieve in a relapsed/refractory disease setting. Hematologic response is required to obtain a cardiac organ response, which is predictive of survival and is an important, if not primary, therapeutic goal. We have previously reported rapid and favorable hematologic response rates with the monoclonal anti-CD38 antibody daratumumab in a cohort of heavily pretreated relapsed/refractory AL patients. The aim of this study was to evaluate cardiac organ response following light chain suppressive therapy with daratumumab in patients with relapsed/refractory AL.

Materials & Methods:Consecutive patients with biopsy-proven AL and cardiac involvement, followed at the Stanford University Amyloid Center, who received daratumumab were retrospectively evaluated for hematologic and cardiac organ response. In accordance with IRB approval, demographic and clinical information was obtained from medical records. Hematologic and cardiac organ response criteria were defined per consensus guidelines in AL (Comenzo et al, Leukemia 2012).

Results: Twelve patients with previously treated AL with cardiac involvement received a median of 12 doses (range 5-18) of single agent daratumumab. The antibody was given intravenously at 16 mg/kg weekly for 8 weeks, followed by every other week infusion for 8 doses and then monthly infusions. The median patient age was 67 and 75% of patients were male. The median number of lines of prior therapy was 3; notably, none of the patients had previously achieved a hematologic complete response to prior therapy including high dose melphalan and autologous stem cell transplant in 2 patients. Ten of 12 patients (83%) achieved a partial hematologic response or better with daratumumab (3 complete responses (25%), 3 very good partial responses (25%), and 4 partial responses (33%)). Median NT-pro BNP was 2516 pg/mL prior to daratumumab therapy. Of all 12 treated patients, seven patients were evaluable for cardiac response based on baseline NT-proBNP >650 ng/L. Of these, 3 patients achieved a cardiac organ response by NT-pro BNP criteria (>30% reduction and >300 ng/l decrease). Two patients had cardiac progression by NT-pro BNP criteria (no echocardiographic progression was observed) despite hematologic response with one patient discontinuing therapy to pursue hospice care. Infusion reactions were observed in 8/12 patients with only 1 grade 3 infusion reaction.

Conclusions: Daratumumab yielded rapid and significant hematologic responses in our retrospective single institution cohort of heavily pretreated AL patients. At a median daratumumab duration of therapy of only 4 months, evidence of cardiac organ improvement was observed. Daratumumab represents a well tolerated and exceptionally promising new treatment for patients with AL amyloidosis; larger prospective trials to evaluate this agent are warranted.