A short low-dose imatinib trial allows rapid identification of responsive patients in hypereosinophilic syndromes.

Although imatinib may be effective in hypereosinophilic syndromes, the exact response kinetics are not known. Imatinib was administered at 100-400 mg/d each week in a 12-week response-oriented schedule, targeting a complete clinical and haematological remission (CR). CR was achieved in 11/23 patients (6/6 with FIP1L1-PDGRFA rearrangement and 5/17 without, P = 0.006), most after 2 weeks of 100 mg/d imatinib. The maximum imatinib dose had no effect in early unresponsive patients. Low-dose, short-course imatinib may represent a rational choice for identifying responsive cases, both within and outside the pre-defined FIP1L1 rearrangement subset.