Allogeneic Hematopoietic Cell Transplantation for Blastic Plasmacytoid Dendritic Cell Neoplasm: a CIBMTR analysis.

Blastic plasmacytoid dendritic cell neoplasm (BPDCN) is a rare hematological malignancy with a poor prognosis and considered incurable with standard conventional chemotherapy. Small observational studies have shown that allogeneic hematopoietic cell transplantation (allo-HCT) offers durable remissions in patients with BPDCN. We conducted an analysis of 164 patients with BPDCN from 78 centers who underwent allo-HCT between 2007-2018 using data reported to the Center for International Blood and Marrow Transplant Research (CIBMTR). Results: Median follow up of survivors was 49 months (range 6-121). 5-year overall survival (OS), disease-free survival (DFS), relapse, and non-relapse (NRM) rates were 51.2% (95% confidence interval [95%CI]: 42.5-59.8%), 44.4% (95%CI: 36.2-52.8%), 32.2% (95%CI: 24.7-40.3%), and 23.3% (95%CI: 16.9-30.4%), respectively. Disease relapse was the most common cause of death. On multivariate analyses, age ≥60 was predictive for inferior OS (hazard ratio [HR]= 2.16, 95% CI 1.35-3.46, p= 0.001), and higher NRM [HR= 2.19, 95% CI 1.13-4.22, p= 0.02]. Remission status at time of allo-HCT (CR2/PIF/Relapse vs CR1) was predictive of inferior OS [HR= 1.87, 95% CI 1.14-3.06, p= 0.01] and DFS [HR= 1.75, 95% CI 1.11-2.76, p= 0.02]. Use of myeloablative conditioning with total body irradiation (TBI) was predictive for improved DFS and reduced risk of relapse. Conclusion: Allo-HCT is effective in providing durable remissions and long-term survival in BPDCN. Younger age and allo-HCT in CR1 predicted for improved survival, while myeloablative conditioning with TBI predicted for less relapse and improved DFS. Novel strategies incorporating allo-HCT are needed to further improve outcomes.