A small subgroup of patients with hypereosinophilic syndrome (HES) demonstrates imatinib-sensitive fusion transcript-the FIP1L1-PDGFRA (F/P+). These cases are currently diagnosed as chronic eosinophilic leukaemia (CEL). In this paper, we screened 77 patients to estimate the frequency of FIP1L1-PDGFRA transcript among patients with unexplained, long-term hypereosinophilia exceeding 1.5 x 10(9)/L and to analyse the clinical and serological features in F/P+ CEL population. The FIP1L1-PDGFRA chimeric protein was detectable in 16 (14 males and 2 females) out of 77 examined HES patients (20%) by RT-PCR. Two patients suffered from cough at diagnosis. Three out of 16 (18%) patients had no organ involvements, in 5-one organ was affected and in the remaining eight cases-at least two. Eosinophilic organ damage/dysfunction identified splenomegaly in the majority of studied patients. We compared clinical and serological features between CEL F/P+ (n = 16) and HES (n = 61) patients. F/P+ cases had significantly increased WBC and absolute eosinophil count (AEC) at diagnosis (p = 0.008 and 0.02), whereas platelet count was decreased in this population (p = 0.03). Serum B12 and tryptase levels were increased (p = 0.002 and 0.004) in CEL F/P+ patients when compared to HES cases whereas serum IL-5 levels were significantly increased in the latter group (p = 0.01). Male gender and splenomegaly occurred more frequent in CEL F/P+ population (p = 0.002 and 0.0007, respectively). Additionally, patients with F/P+ CEL (n = 16) were compared with F/P- CEL (n = 8). The latter group, was significantly older, had lower AEC and higher platelet count. In conclusion, significant clinical symptoms are infrequent present and splenomegaly remains the most common organ involvement in patients with CEL expressing F/P fusion transcript. Our study confirmed the long-term remission on imatinib in this patient population.
(c) 2009 John Wiley & Sons, Ltd.