Introduction Immune thrombotic thrombocytopenic purpura (iTTP) is an acquired, fatal microangiopathy if untreated. Randomized controlled trials (RCT's) demonstrated faster time-to-response with adding caplacizumab to standard of care (SOC). However, concerns about RCT selection bias and the high cost of caplacizumab warrant examination of all evidence, including real-world observational studies. Methods In this systematic review and meta-analysis, we searched the literature for comparative

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... es evaluating SOC with or without caplacizumab for the treatment of iTTP. We assessed risk-of-bias using the Cochrane RoB-2 tool (RCT's) and Newcastle-Ottawa Scale (observational studies). The primary efficacy outcome was all-cause mortality, and the primary safety outcome was treatment-emergent bleeding. Secondary outcomes included exacerbation and relapse, refractory iTTP, and time-to-response. Results We included two high-quality RCT's and three observational studies at high-risk-of-bias comprising 632 participants. Compared with SOC, caplacizumab was associated with a non-significant reduction in the RR (0.21 [CI 0.05-1.74]) of death in RCT's and observational studies (RR 0.62 [CI 0.07, 4.41]). Compared with SOC, caplacizumab was associated with an increased risk of bleeding in RCT's (RR 1.37 [CI 1.06, 1.77]). In observational studies, the risk of bleeding was not significantly increased (RR 7.10 [CI 0.90, 56.14]). Addition of caplacizumab was also associated with a significant reduction in refractory iTTP and exacerbation, increased risk of relapse, and shortened response time. Conclusion Frontline addition of caplacizumab does not significantly reduce all-cause mortality compared with SOC alone, although it reduces refractory disease risk, shortens time-to-response, and improves exacerbation rates, at the expense of increased relapse and bleeding risk.