Adverse impact of delay of platelet recovery after autologous hematopoietic cell transplantation for aggressive non-Hodgkin lymphoma and multiple myeloma

Background aims: The prognostic impact of platelet recovery after autologous hematopoietic cell transplantation (AHCT) on clinical outcomes remains to be elucidated. We aimed to clarify the impact of platelet recovery on clinical outcomes, risk factors of delayed platelet recovery and the necessary dose of CD34⁺ cells for prompt platelet recovery in each patient. Methods: Using a nationwide Japanese registry database, we retrospectively analyzed clinical outcomes of 5222 patients with aggressive non-Hodgkin lymphoma (NHL) or multiple myeloma (MM). Results: At a landmark of 28 days after AHCT, a delay of platelet recovery was observed in 1102 patients (21.1%). Prompt platelet recovery was significantly associated with superior overall survival (hazard ratio [HR] 0.32, P < 0.001), progression-free survival (HR 0.48, P < 0.001) and decreased risks of disease progression (HR 0.66, P < 0.001) and non-relapse/non-progression mortality (HR 0.19, P < 0.001). The adverse impacts of a delay of platelet recovery seemed to be more apparent in NHL. In addition to the dose of CD34⁺ cells/kg, disease status, performance status and the hematopoietic cell transplant-specific comorbidity index in both diseases were associated with platelet recovery. We then stratified the patients into three risk groups according to these factors. For the purpose of achieving 70% platelet recovery by 28 days in NHL, the low-, intermediate- and high-risk groups needed more than 2.0, 3.0 and 4.0 × 10⁶ CD34⁺ cells/kg, respectively. In MM, the low-risk group needed approximately 1.5 × 10⁶ CD34⁺ cells/kg, whereas the intermediate- and high-risk groups required 2.0 and 2.5 × 10⁶ CD34⁺ cells/kg to achieve about 80% platelet recovery by 28 days. Conclusions: A delay of platelet recovery after AHCT was associated with inferior survival outcomes.