Response and resistance to cladribine in patients with advanced systemic mastocytosis: a registry-based analysis.

We sought to evaluate the efficacy of the purine analogue cladribine in 79 patients with advanced systemic mastocytosis (AdvSM) using data from the 'German Registry on Disorders of Eosinophils and Mast Cells (GREM)'. The overall response rate according to modified Valent criteria (46 evaluable patients) for first- (1L) and second-line (2L) cladribine treatment was 41% (12/29) and 35% (6/17, P = 0.690), respectively, and the median overall survival (OS, all patients evaluable) was 1.