Background: Conventional AlloTx for MM is associated with TRM exceeding 20%. Non-myeloablative AlloTx (NST) utilizes the known graft-vs-myeloma (GVM) effect in an attempt to eradicate minimal residual disease. Preliminary studies of NST in MM demonstrated significant CR and low 100 day post-NST TRM (

Badros et al
). However, even though response rates were high, the vast majority of pts with significant MM disease at the time of transplant, relapsed within the first year. To provide maximal tumor cytoreduction to allow for a subsequent GVM effect, the ECOG designed a Phase II trial of AHSCT for maximal tumor cytoreduction followed by a matched sibling NST to allow for a GVM effect.

Methods: The study was designed as a two-stage process based upon early transplant mortality in the first 100 days. Eligibility included pts treated as part of induction therapy or salvage therapy. Chemotherapy responsive disease was not required. Only matched sibling donors were allowed. Pts must have had adequate PS and physiologic organ function. After stem cell mobilization, pts received melphalan 200 mg/m2 with AHSCT. Pts underwent NST 100–182 d post-AHSCT following fludarabine 30 mg/m2 daily × 5 and cyclophosphamide 1 g/m2 for 2 days. GVHD prophylaxis included cyclosporine and corticosteroids. For pts with acute GVHD, Zenapax 1 mg/kg for 5 doses q 3 d was recommended. GM-CSF was incorporated post-AHSCT and NST. The primary endpoints were day 100 TRM, early graft failure, extent of acute GVHD, toxicities, DFS and OS. The study was suspended for 6 mo after the first 19 pts to evaluate early TRM-no early TRM was observed and the study was re-opened.

Results: From 5/3/01 to 1/14/05, 32 pts from 10 institutions were enrolled on the study. 23 patients, median age 51 (range 32–64) completed both transplants (28% drop-out rate): 7 (30%) CR (2 in CCR), 11 (48%) PR and 2 (9%) NR and 3 (13%) NE as the best overall response. Of the 32 pts who completed AHSCT, there were 12 grade 4 toxicities pre-NST; 11/23 pts had grade 4 toxicities post-NST. Acute grade III/IV GVHD was observed in 4 (17%); chronic GVHD was observed in 9 pts (39%): 5 limited; 4 extensive resulting in 3 CR (33%), 1 CCR, and 3 PR (33%). 1 pt (4%) had graft-failure. Two pts (8.7%; 95% CI 1.6%, 24.9%) had TRM prior to day + 100 post-NST. With a median follow up of 3.5 years from registration, the median PFS was 4.4 years and the 2-year survival rate was 78% (95% CI: 61% ∼ 95%) for the 23 pts who completed both transplants.

Conclusions: AHSCT followed by NST is feasible in a Cooperative Group setting with a low early TRM. The PFS and OS were superior to historical reports for single and tandem AHSCT. AHSCT-NST tandem transplants resulted in a 78% overall response, including 30% CR (2/7 CCR) - similar to other reports for AHSCT-NST. 3/9 pts with chronic GVHD achieved CR demonstrating the GVM effect. However, a plateau in PFS or OS was not observed indicating that the GVM effect is not sufficient to produce long- term disease control and is unlikely curative using this treatment schema. Future studies should include novel therapies to induce better responses pre-transplant and consideration for post-NST maintenance to further eradicate MRD while allowing for GVM.

Author notes

Disclosure: No relevant conflicts of interest to declare.