Long Term Outcomes of Mepolizumab Treatment Compared to Conventional Therapy for Subjects with HES
Sunday, March 6, 2016
South Exhibit Hall H (Convention Center)
Fei Li Kuang, MD PhD, Paneez Khoury, MD, JeanAnne M Ware, CRNP, Amy D. Klion, MD
Rationale: Whereas clinical trials have demonstrated the safety and utility of mepolizumab (anti-IL-5 antibody) as a steroid-sparing agent in PDGFRA-negative subjects with steroid-responsive HES, the efficacy of mepolizumab in preventing disease progression as compared to conventional therapy in the broader group of PDGFRA-negative patients with HES has not been explored to date.

Methods: Subjects with PDGFRA-negative HES followed for a minimum of 5 years (or deceased within 5 years of the initial visit) on an IRB-approved protocol designed to evaluate subjects with eosinophilia were identified by retrospective chart review. Clinical characteristics and responses to therapy were recorded.  For subjects who received mepolizumab, the initial visit was defined as the mepolizumab initiation visit.

Results: Among the 251 subjects with PDGFRA-negative HES, 90 met follow-up criteria, of which 27 received mepolizumab therapy (MEPO).  Nineteen (70%) of the MEPO subjects demonstrated a complete response (AEC <1500/mm3 and symptomatic improvement on mepolizumab monotherapy) and 7 additional subjects showed a partial response.  Median months of follow-up, age at first visit, gender, and peak eosinophil counts were not significantly different between MEPO and non-MEPO subjects.  However, MEPO subjects had failed more therapies prior to the initial visit (p=0.0002). Mortality was 7.7% (2/27) in the MEPO group and 20.6% (13/63) in the non-MEPO group (p=0.21).  Three subjects in each group were diagnosed with a malignancy.

Conclusions: Although mepolizumab was effective in lowering eosinophil counts and improving symptoms in subjects with treatment-refractory HES followed for ≥5 years, mortality was not significantly decreased as compared to subjects receiving conventional therapy.