Transplantation Strategies in Treatment of Primary Plasma Cell Leukemia in Germany-A Multi-Center Analysis.

OBJECTIVES: Primary plasma cell leukemia (pPCL) is a rare disease with poor outcomes. As data on randomized phase-III trials are lacking, treatment recommendations are predominately based on retrospective analyses incorporating time periods with outdated therapies. Thus, the optimal consolidation strategy remains to be defined. METHODS: We conducted a retrospective, multi-center analysis with 49 transplant-eligible patients diagnosed with pPCL between 2011 and 2025 focusing on different stem cell transplantation (SCT) strategies as consolidation treatment in first remission: single autologous (auto) or single allogeneic (allo) SCT versus patients with tandem cell therapy strategies (auto-auto, allo-auto, auto-chimeric antigen receptor therapy). RESULTS: The median follow-up after first SCT was 31 months. The cumulative incidence of initiating next treatment was lower after tandem cell therapy compared to single SCT (at 12 months: 42% vs. 57%, p = 0.006). Moreover, in a multivariable analysis incorporating cytogenetic risk and response to induction therapy, tandem transplantation strategies tended to be the only independent predictor for prolonged time to next treatment (TTNT, p = 0.077). Noteworthy, differences in TTNT between patients with a single SCT and patients with tandem cell therapy did not translate into an improved overall survival, possibly due to potent salvage therapies. CONCLUSIONS: Our data support recent recommendations advising treating patients with tandem transplantation regimes.