Clinical Characteristics and Survival Outcomes of Patients With Primary and Secondary Plasma Cell Leukemia According to the 2021 Definition: A Single Center Retrospective Study.

Introduction: Plasma cell leukemia (PCL) is a rare malignancy with poor overall survival (OS). Recently, its diagnostic criteria were revised by lowering the threshold of circulating plasma cells from ≥ 20% to ≥ 5%.

Methods: Between 2010 and 2024, patients with primary PCL (pPCL) and secondary PCL (sPCL) were identified at a tertiary center. We retrospectively analyzed baseline characteristics, treatment, and survival in months (m).

Results: We identified 30 patients with pPCL and 29 patients with sPCL. The median time to sPCL in patients who received Daratumumab (Dara)-containing regimens for multiple myeloma was 46.8m compared with 12.3m in patients who did not (P=0.007). Of the whole cohort, 51.9% received an induction regimen with novel agents without chemotherapy. Of the evaluable patients with pPCL and sPCL, 82.1% (23/28) and 64.7% (11/17) achieved partial response or better respectively. Median progression free survival was significantly worse in patients with sPCL than pPCL (2.2 vs. 38.3 months; HR 0.16; 95% CI (0.07-0.35), P < .001). Median OS was also worse in patients with sPCL compared with pPCL (3.1 months vs. NR [not reached]; HR 0.09; 95%CI 0.04-0.23, P < .001). The median post-SCT survival for patients with pPCL was NR compared with 6.7m for patients with sPCL (HR 0.17; 95% CI (0.03-0.83), P = .03). Dara-refractory status was associated with worse OS (HR 5.63; 95% CI (2.75-11.51), P < .0001).

Conclusion: Outcomes of pPCL are improving but remain dismal for sPCL. We explored the role of novel agents, especially Dara, in the treatment of PCL. More prospective trials are needed to improve its outcomes.