Haploidentical allogeneic hematopoietic cell transplantation for multiple myeloma using post transplant cyclophosphamide GVHD prophylaxis

Allogeneic Hematopoietic Cell Transplantation (allo-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 is are available data regarding this treatment. We analyzed survival outcomes of 30 heavily pretreated MM patients who received haplo-HCT with post-transplant cyclophosphamide (PT-Cy) as graft-versus-host-disease (GVHD) prophylaxis. Median neutrophils and platelets engraftment at day +30 were 87% (95% confidence interval [CI]: 66-95%) and 60% (95%CI: 40-75%), respectively. The cumulative incidence of relapse or progression of disease (PD) and non-relapse mortality (NRM) at 18 months were 42% (95% CI: 23-59%) and 10% (95%CI: 2-24%), respectively. The cumulative incidence of grade II-IV acute GVHD at day +100 was 29% (95%CI: 14-47%). The cumulative incidence of chronic GVHD at 18 months was 7% (95% CI: 1-21%). With a median follow-up in survivors of 25 months (range 15-73 months), the 18-month progression-free survival (PFS) and overall survival (OS) were 33% (95%CI: 17-50%) and 63% (95%CI: 44-78%), respectively. No differences were observed between peripheral blood (PBSC) and bone marrow (BM) graft in terms of engraftment, GVHD or PD incidence. Chemorefractory disease at transplant was associated with a lower/reduced 18-month PFS (9% vs 47%, p=0.01) and OS (45% vs 74%, p=0.03). This was explained by a higher PD incidence (55% vs 33%, p=0.05). In these multicenter study, we report encouraging results with haplo-HCT for patients with heavily pretreated MM.