Characterization of different regimens for initiating anagrelide in patients with essential thrombocythemia who are intolerant or refractory to their current cytoreductive therapy: results from the multicenter FOX study of 177 patients in France

OBJECTIVES: To identify switch modalities used when initiating second- or third-line anagrelide for essential thrombocythemia (ET), assess whether anagrelide is initiated consistently with Summary of Product Characteristics (SPC) recommendations, and determine whether different observed switch regimens have any relationship with maintenance, platelet response, or tolerability. METHODS: This observational study was conducted across 43 centers in France. High-risk patients (>60 yr of age and/or history of thrombosis and/or platelet count >1000 × 10(9)/L) with ET starting second- or third-line anagrelide therapy were identified and monitored for 6 months. RESULTS: A total of 177 patients were enrolled. The SPC-recommended starting dose (1 mg/d) was used in 52.6% of patients; 0.5 mg/d was used in 41.1%. 77.1% of patients underwent an anagrelide dose increase during the study. At 6-month follow-up, 84.7% of patients (n = 144/170) were still receiving anagrelide; 70.6% (n = 120/170) achieved a platelet response. A higher proportion of patients who discontinued previous cytoreductive therapy (CRT) after initiating anagrelide achieved a platelet response (n = 34/39, 87.2%) vs. patients who discontinued their previous CRT before anagrelide initiation (n = 77/115, 67.0%). Platelet response rates were higher in patients whose anagrelide initiation was consistent (n = 100/133, 75.2%) vs. inconsistent (n = 20/37, 54.1%) with the SPC. The incidence of adverse drug reactions was lower in patients whose anagrelide treatment was consistent (n = 52/133, 39.1%) vs. inconsistent (n = 25/37, 67.6%) with the SPC. CONCLUSIONS: To our knowledge, the FOX study provides the first comprehensive real-world data on the modalities used when switching from previous CRT to anagrelide. Highest platelet responses were observed when previous CRT was discontinued after anagrelide initiation or when anagrelide was initiated consistently with the SPC. Safety data corresponded with the SPC.