Prevalence of paroxysmal nocturnal hemoglobinuria (PNH) cells in patients with myelodysplastic syndromes (MDS), aplastic anemia (AA), or other bone marrow failure (BMF) syndromes: Interim results from the EXPLORE trial

Abstract

7082 Background: In patients with PNH, lack of the glycophosphatidylinositol (GPI)-anchored terminal complement inhibitor CD59 on hematopoietic stem cells results in chronic intravascular hemolysis, kidney and pulmonary disorders, thrombosis, and shortened life span. Presence of even minor populations of PNH cells in AA or MDS patients is medically important as it may indicate a higher likelihood of response to immunosuppressive therapy. We conducted the first large multicenter, point-prevalence study (EXamination of PNH, by Level Of CD59 on REd and white blood cells [EXPLORE]) of PNH cells in patients with AA, MDS, or other BMF syndromes. Here we report an interim analysis. Methods: A central laboratory conducted high-sensitivity flow cytometry utilizing a combination of GPI-linked antibodies (CD59, CD24, and CD14) and fluorescent aerolysin (FLAER) to identify GPI anchor-deficient PNH cells in RBC and WBC resulting in 0.01% sensitivity. The primary endpoint was percentage of patients who had a PNH WBC clone ≥1%. Results: Among 5,212 patients screened, 4,500 (86.3%) were MDS patients, 413 (7.9%) were AA patients, and 356 (6.8%) had other BMF syndromes. Approximately 1/4 (24.5%) of patients with AA, 1.2% with MDS, and 4.6% with other BMF were newly found to have a significant PNH clone ≥ 1%. Many of the newly identified clones were of clinical significance as the median PNH clone size was 11.1% in AA patients, 16.3% in MDS patients, and 32.6% in patients with other BMF. Presence of PNH cells (≥ 0.01%) was common in all examined BMF types: 70% of AA patients, 55% of MDS patients and 55% of patients with other BMF. PNH cells were identified in all MDS subtypes represented in the trial. Conclusions: Interim analysis from this first large multicenter study demonstrates that PNH cells are present in a majority of patients with AA, MDS, and other BMF. A spectrum of PNH clone sizes was noted in patients with each form of BMF. Screening patients with BMF with high-sensitivity flow cytometry for PNH cells may guide treatment options for the underlying BMF and/or PNH. The EXPLORE trial continues to enroll patients with AA. (EXPLORE Clinical Study Abstract 1/6/2009) [Table: see text]