A Phase I Trial of Zevalin Radioimmunotherapy with High-Dose Melphalan (HDM) and Autologous Stem Cell Transplant (ASCT) for Multiple Myeloma (MM)

Abstract 3095 Background: Although HDM is the standard conditioning for pts with MM undergoing ASCT, it is not sufficient for cure. In an effort to improve upon this standard, we added escalating doses of Y-90 Zevalin (a murine IgG1 kappa monoclonal antibody Ibritumomab conjugated to Y-90) to HDM in a standard 3+3 phase I trial design. Y-90 is a beta-emitting radioisotope with a path length of 5 mm allowing it to target CD20+ cells and bystander cells within 5 mm. Methods: Eligibility included being a candidate for ASCT. Consenting patients (pts) received: day -22, rituximab 250 mg/m2 with In2B8 for scanning; day -14, rituximab 250 mg/m2 with escalating doses of Y90-Zevalin; day -2 and -1, melphalan 100 mg/m2/day; day 0, at least 2 × 10(6) CD34/kg stem cells; and GM-CSF until ANC engraftment. The 6 dose levels (DL) were (in Gy): 10; 12; 14; 16; 18; and 20. Dose limiting toxicity (DLT) was defined as: sustained pulmonary or liver toxicity (grade3; 96 hours duration or VOD that does not resove by day 30); delayed engraftment (ANC Results: Thirty pts have been accrued: DL1, 3; DL2, 3; DL3, 3; DL4, 6, DL5, 6; DL6, 6. The median age of patients was 59 (range 32, 73), and 70% were male. 60% had ASCT as primary therapy. The other patients were transplanted in chemosensitive relapse (n=3), chemoresistant relapse (n=7), and untested relapse (n=2). Median time from diagnosis to protocol therapy was 10.4 months (range 3.5, 94.3). Five pts had prior radiation therapy, and 11 had prior ASCT. Maximum tolerated dose (MTD) of Zevalin with fixed dose melphalan 200 mg/m2 was DL 5 (18 Gy) which amounted to 168 mCi (124, 182) administered. No DLTs were observed at DL 1, 2, 3, or 5. There was 1 DLT at DL 4, comprising hepatic failure (gr 5) CMV viremia (gr 3), and delayed engraftment, in a 73 yo patient with chemoresistant relapsed disease, and 2 DLTs at DL 6. These DL 6 DLTs included: 1) fatal bowel necrosis (day 12 post ASCT) in a 67 yo patient with relapsed refractory MM and history of CAD, ischemic colitis, DM; and 2) fatal biopsy proven venoocclusive disease (gr 5), which began day 91 post ASCT in a 62 yo patient with primary refractory MM, peri-mobilization S. aureus bacteremia with septic embolic, and line associated venous thrombosis. Overall, gr 3 or higher AEs were observed in 100% of pts. Non-heme gr 4 AEs were seen in: DL1, 1; DL2, 2; DL3, 0; DL4, 1; DL5, 0; DL6, 4. Median time to ANC >=500 and plts>=50 was 11 (range 8, 17) and 15 days (range 11, 89). Confirmed response rates from immediately pre-protocol to best confirmed response were: CR, 5; VGPR, 5; continued VGPR, 4, and continued PR, 7. If one includes best confirmed response from baseline for those patients using transplant as primary consolidation, 4 PRs are upstaged to VGPRs. Median follow-up for all pts is 24.5 months (0.8, 64.8), and 10 pts have died. The median PFS for pts proceeding to early and delayed ASCT was 30.4 months (95%CI 4.1-NR) and 10.3 months (95%CI 2.8–21.7), respectively. The median OS for pts proceeding to early and delayed ASCT was not attained and 11.4 months (95%CI 2.8-NA), respectively. Conclusions: For patients with multiple myeloma, the MTD of Zevalin with fixed high-dose melphalan is 18 Gy. The combination of a VGPR plus continued VGPR rate of 60%, a median PFS of 13.1 months, and a 73% 1 year OS rate make this a regimen worthy of further study. Disclosures: Kumar: Merck: Consultancy, Membership on an entity9s Board of Directors or advisory committees.