Haploidentical Allogeneic Hematopoietic Cell Transplantation for Multiple Myeloma Using Post-Transplantation Cyclophosphamide Graft-versus-Host Disease Prophylaxis

Allogeneic (allo) hematopoietic cell transplantation (HCT) currently represents the only potentially curative therapy for patients affected by multiple myeloma (MM). Up to 30% of patients in western countries do not have a matched donor. Haploidentical HCT (haplo-HCT) may be an option, but currently, there are little available data regarding this treatment. We analyzed survival outcomes of 30 heavily pretreated MM patients who received haplo-HCT with post-transplantation cyclophosphamide as graft-versus-host-disease (GVHD) prophylaxis. Median neutrophil and platelet engraftments at day +30 were 87% (95% confidence interval [CI], 66% to 95%) and 60% (95% CI, 40% to 75%), respectively. The cumulative incidences of relapse or progression of disease (PD) and nonrelapse mortality at 18 months were 42% (95% CI, 23% to 59%) and 10% (95% CI, 2% to 24%), respectively. The cumulative incidence of grade II to IV acute GVHD at day +100 was 29% (95% CI, 14% to 47%). The cumulative incidence of chronic GVHD at 18 months was 7% (95% CI, 1% to 21%). With a median follow-up in survivors of 25 months (range, 15 to 73 months), the 18-month progression-free survival (PFS) and overall survival (OS) were 33% (95% CI, 17% to 50%) and 63% (95% CI, 44% to 78%), respectively. No differences were observed between peripheral blood and bone marrow graft in terms of engraftment, GVHD, or PD incidence. Chemorefractory disease at transplantation was associated with a lower/reduced 18-month PFS (9% versus 47%, P = .01) and OS (45% versus 74%, P = .03). This was explained by a higher PD incidence (55% versus 33%, P = .05). In this multicenter study, we report encouraging results with haplo-HCT for patients with heavily pretreated MM.