Prolonged clinical response to vincristine treatment in two patients with idiopathic hypereosinophilic syndrome.

Idiopathic hypereosinophilic syndrome (HES) is a rapidly progressive disease that can result in death within weeks to months of diagnosis in untreated patients. We report two pediatric cases of HES. One patient has remained clinically and hematologically stable for 9 years with vincristine and 6-thioguanine (6TG), and the other has received vincristine alone for 6 months with a good response. The use of long-term vincristine and 6TG or vincristine alone has not been previously reported in the management of HES in children. Vincristine administered every 3-4 weeks with or without 6TG can produce a reduction in the overall white cell count and improvement of symptoms of hypereosinophilia. Although the mortality of patients with HES is high, aggressive treatment can result in significant clinical benefit and improved prognosis in children with this syndrome.