Bortezomib for rituximab-refractory immune-mediated thrombotic thrombocytopenic purpura in the caplacizumab era: an Italian multicenter study

Background: Immune-mediated thrombotic thrombocytopenic purpura (iTTP) patients are not responsive to standard rituximab in approximately 10% to 15% of cases, and oral immunosuppressants showed controversial results with significant toxicity. Targeting plasma cells with bortezomib appears promising, but the available evidence is scarce and stems only from isolated reports in the precaplacizumab era. Objectives: To evaluate the safety and efficacy of bortezomib in rituximab-refractory iTTP patients. Methods: We conducted a retrospective observational multicenter study among 13 Italian iTTP treating centers, collecting data from May 2017 to May 2023 (caplacizumab was licensed in Italy in January 2020). Results: Bortezomib was effective in 10/17 patients (59%). Eleven were treated in the acute phase (9/11 responders, 82%, allowing discontinuation of caplacizumab in 5/6 treated patients), and 7 during clinical remission (2/7 responders, 28%). Responses occurred at a median time of 30 days, but 3 patients responded after 4 months. The median duration of response was 22 months (IQR, 10-38), still ongoing in 6 patients at the time of data cutoff. Responders had fewer previous acute iTTP episodes than nonresponders (median [IQR], 1 [1,2] vs 5.5 [2–7]; P = .03). Eight subjects (47%) reported toxicities, mostly in those treated with ≥2 cycles. Conclusion: Durable responses to bortezomib were registered in about 60% of multirefractory iTTP patients with mild to moderate toxicities. The occurrence of late responses (ie, after 30 days) suggests a “watchful waiting” approach after bortezomib treatment.