Real-World Treatment Patterns and Outcomes Among Patients with Primary Hemophagocytic Lymphohistiocytosis with and without Infection at Diagnosis and Treated with Emapalumab: The Real-HLH Study

Background: Primary hemophagocytic lymphohistiocytosis (pHLH), a rare, life-threatening, hyperinflammatory syndrome, characteristically shows overproduction of interferon gamma (IFNγ). Since FDA approval of emapalumab for refractory, recurrent, or progressive pHLH or intolerance with conventional therapy, there are limited real-world data on its use. The REAL-HLH study assessed real-world treatment patterns and outcomes among patients treated with emapalumab. Emapalumab treatment patterns and outcomes in the real world among patients with pHLH with or without infection at HLH diagnosis are presented.

Methods: Data were extracted via a retrospective medical chart review of patients with pHLH treated with ≥1 dose of emapalumab between Nov. 20, 2018, and Oct. 31, 2021, across 33 US hospitals from time of emapalumab initiation to end of data availability, death, or study end (Dec. 31, 2021). Data are presented as summary statistics and comparisons using χ ² tests.

Results: Forty-six of 105 enrolled patients met the pHLH classification criteria; 25/46 (54.3%) had infection at diagnosis with viral infections being most common (18/25; 72.0%). Baseline characteristics are provided in Table 1. The median (range) times from HLH diagnosis to emapalumab initiation and treatment duration with emapalumab for the 2 groups are provided in Table 2. Median (range) starting, maximum single, and cumulative administered dose of emapalumab for the 2 groups are provided in Table 2. Overall survival rates from emapalumab initiation for patients with (18/25; 72.0%) and without infection (16/21;76.2%) were comparable; p=0.747. A greater proportion of eligible patients without infection (15/19; 78.9%) received hematopoietic stem cell transplantation (HSCT) compared with those with infection (16/23; 69.6%), but the difference was not statistically significant (p=0.491).

Conclusion: This is the first study to report real-world treatment patterns with emapalumab across a diverse patient population with pHLH with or without infection at diagnosis. Over 54% of the patients with pHLH presented with infection at diagnosis. The infection status at diagnosis did not affect the overall survival rate and the proportion of patients proceeding to HSCT after emapalumab treatment.