Updated Results of a Phase II Study of Lenalidomide-Elotuzumab As Maintenance Therapy Post-Autologous Stem Cell Transplant (AuSCT) in Patients (Pts) with Multiple Myeloma (MM)

Background: Lenalidomide (LEN) monotherapy has been effective in extending progression free survival (PFS) after myeloablative AuSCT in pts with MM. Elotuzumab (ELO), a humanized IgG1 immunostimulatory monoclonal antibody against signaling lymphocytic activation molecule F7 (SLAM F7), is FDA approved in combination with LEN and dexamethasone (DEX) for treatment of MM pts who have received 1-3 prior therapies. The objective of this phase 2 trial is to evaluate the efficacy and safety of adding ELO to LEN as maintenance therapy post-myeloablative AuSCT. We report updated results of the primary (PFS) and secondary (overall survival [OS] and toxicity) endpoints.

Patients and Methods: Between 4/15/2015-1/27/2016, 27 evaluable pts were treated on 28 day cycles with ELO, 10 mg/kg iv weekly for cycles 1-2, q2weeks for cycles 3-6, then 20 mg/kg once monthly for cycles 7+. Pts enrolled after 1/28/2016 (n=57 pts) have received ELO, 10 mg/kg IV weekly for cycles 1-2, and 20 mg/kg on day 1 from cycle 3 until disease progression (PD). LEN has been dosed at 10 mg/day for cycles 1-3, with a dose increase to 15 mg/day at physician discretion starting with cycle 4, in the absence of non-hematologic toxicity > grade 1 and significant cytopenias (ANC < 1000/mL, platelet count < 100,000/ml). For the 1^st 8 weeks, pts <75 yrs receive 28 mg of DEX 3-24 hours pre-infusion, while pts ≥75yrs receive 8 mg; pts receive 4-10 mg iv DEX immediately pre-infusion for all cycles. Pts also receive zoster and thromboembolic prophylaxis commensurate with standard recommendations.

The study's primary endpoint is PFS, defined as time from AuSCT to PD or death (whichever occurs first), or time of last contact. Secondary objectives are best response, OS, incidence of second primary malignancies (SPMs) and adverse event (AE) profile. Total enrollment of 100 pts is planned. Patients are followed until death, withdrawal of consent or removal from study. Eligible pts received ≤2 lines of induction therapy, and are 60-210 days post-AuSCT.

Results: Pts (n=84) have been treated for a median of 16 cycles (2-43). At study entry, 27 (32%) had complete response (CR), 36 (43%) had very good partial remission (VGPR), 20 (24%) had partial remission (PR) and 1 (2%) had minor remission (MR). Best response achieved to date on study is CR in 44 pts (52%), VGPR in 31 pts (37%) and PR in 9 pts (11%). For those who have converted to CR on study, median time to CR was 2 months. Of 22 pts in CR who have been tested for minimal residual disease (MRD) to date, 20 are negative by flow cytometry (minimum of 2 million cells evaluated). Three of 20 have converted from VGPR to MRD negativity while on study.

With a median follow up of 23 months, 96% of pts (n=81) remain alive. Ten pts have had PD; of these, 6 had high risk cytogenetics. Two died of PD while receiving salvage therapy. One additional pt died on study in VGPR, after developing acute cerebral encephalopathy with refractory status epilepticus of unclear etiology. Four pts withdrew for personal reasons, 4 were removed at physician discretion (prolonged cytopenias [1], drug rash [1], worsening memory impairment [1], therapy related myelodysplastic syndrome (t-MDS) [1]), and 2 lost insurance coverage. Estimated 3 year PFS is 81%. High risk cytogenetics adversely affected PFS (p=0.02).

Grade 3-4 Hematologic AEs (no. of pts) were: neutropenia 32% (27), febrile neutropenia 15% (13), thrombocytopenia 8% (7), and anemia 7% (6). Grade 3-4 non-Hematologic AEs (no. of pts): respiratory infections 17% (15), diarrhea 14% (12), fatigue 13% (11), other infections 8% (7), peripheral neuropathy 7% (6), myalgias 6% (5), nausea/vomiting 4% (3), dizziness 2% (2), memory impairment 2% (2), maculopapular rash 2% (2), edema 1% (1). SPMs include intra-epidermal adenocarcinoma of the neck (1), mucinous appendiceal neoplasm (1), t-MDS (1), prostate cancer (1), and melanoma (1). Renal cell carcinoma was diagnosed in 1 pt, 15 months after removal from study for PD.

Conclusions: Lenalidomide-elotuzumab is a well-tolerated maintenance therapy during which 33% of 84 pts had improvement in quality of response while on therapy, including 20% who converted to CR. The number of pts experiencing improvement may be underestimated due to ELO interference with paraprotein measurement on electrophoretic studies. Additional follow up is required to determine if the improved quality of responses translate into improvements in PFS and OS. Available data supports conduct of a Phase 3 trial.

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