Eculizumab Protects Against TE and Prolongs Survival in Patients with Paroxysmal Nocturnal Hemoglobinuria: An International PNH Registry Study

Paroxysmal nocturnal hemoglobinuria (PNH) is a chronic and life-threatening hematopoietic stem cell disorder characterized by uncontrolled complement-mediated hemolysis. PNH, in large part due to chronic hemolysis and platelet hyperactivation, is associated with thromboembolism (TE), one of the leading causes of disease mortality. Eculizumab, a monoclonal antibody that inhibits terminal complement activation, has been shown in clinical trials to reduce hemolysis and the incidence of TE. The International PNH Registry provides the opportunity to understand from real world experience the impact of eculizumab on TE reduction in PNH patients.

To assess the risk factors for TE and mortality in PNH patients enrolled in the Registry and to assess the effectiveness of eculizumab in reducing PNH-associated TEs.

Patients are eligible for the Registry if they have a detectable PNH clone, regardless of disease severity, comorbidities, or treatments (past, current or planned). As of June 30, 2012, there were 1547 patients enrolled from 25 countries on 5 continents. Patients were excluded from analysis if they were missing key demographic variables or dates of eculizumab use, or did not yet have follow-up information. The cumulative incidence of TE was determined using competing risks methods to take into account bone marrow transplantation and death, while Kaplan-Meier methods were used for the cumulative incidence of mortality. Risk factors for TE and mortality were explored using a Cox proportional hazards model with stepwise selection (the significance level was relaxed to P=0.20 due to the small number of events for analysis). Variables examined in the models included: ethnicity; prior TEs, bone marrow disorders, impaired renal function, impaired hepatic function (IHF), abdominal pain, dysphagia, dyspnea, easy bruising/bleeding, fatigue, headache, hemoglobinuria, Karnofsky performance score, granulocyte clone size and lactate dehydrogenase (LDH) at enrollment, red blood cell (RBC) transfusions 6 months prior to enrollment as a marker for hemolysis, and treatments after enrollment (eculizumab and warfarin/heparin).

The mean age of the 1047 patients eligible for analysis was 45 years; 537 patients (51.3%) were female and 868 were Caucasian (82.9%). Anti-coagulants (heparin/warfarin) were used by 28% of patients and eculizumab was used by 51% during follow-up (18% used both). During a mean (SD) follow-up of 22.5 (18.4) months, 16 patients had a TE and 51 were deceased. Patients taking eculizumab during follow-up had a cumulative incidence of TE at 1 year of 0.41% and 1.35% at 2 years, while patients not taking eculizumab had TE incidence of 1.70% and 2.61% at 1 and 2 years, respectively. In the multivariate Cox model, the greatest associations with TE were RBC transfusions in the 6 months before enrollment (hazard ratio [HR]=9.61), history of IHF (HR=4.78), dyspnea (HR=2.42) and headache (HR=2.33) at enrollment. While controlling for these variables, eculizumab had a significant protective effect (HR=0.23, 95% CI = 0.08–0.66). The cumulative incidence of mortality in eculizumab-treated patients was 2.31% and 4.21% at 1 and 2 years, while in untreated patients it was 4.40% and 7.01%, respectively. In the multivariate model of mortality, the greatest associations were age 60+ years (HR=4.72), Karnofsky score <80 (HR=2.34), fatigue at enrollment (HR=1.94), and recent RBC transfusion (HR=1.75). While controlling for these variable, eculizumab had a significant protective effect (HR=0.41, 95% CI = 0.23–0.73).

This analysis of a large international cohort of ‘real world’ patients with PNH showed that eculizumab is associated with a significantly reduced risk of TE and mortality, consistent with prior research. Recent RBC transfusion, a surrogate marker for hemolysis, was associated with increased risk of TE and mortality. Several symptoms and hepatic dysfunction also showed increased risks for these outcomes. As might be expected, older age and low performance status were associated with mortality. These data should be interpreted within the context of a contemporary cohort of PNH patients who may or may not be treated (with either eculizumab and/or anticoagulation). These analyses are limited due to small number of TE and mortality outcomes.

Muus:Alexion Pharmaceuticals : Sat on advisory board of Alexion Pharmaceuticals. Other. Urbano-Ispizua:Alexion Pharmaceuticals, Inc: Membership on an entity's Board of Directors or advisory committees. Maciejewski:NIH: Research Funding; Aplastic Anemia&MDS International Foundation: Research Funding. Kanakura:Shire: Consultancy. Rosse:Alexion Pharmaceuticals, Inc: Consultancy, Membership on an entity's Board of Directors or advisory committees. Khursigara:Alexion Pharmaceuticals, Inc: Employment. Bedrosian:Alexion Pharmaceuticals: Employment, Equity Ownership. Hillmen:Alexion Pharmaceuticals, Inc: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees.