Abstract
Background
Patients with congenital low-flow vascular malformations (capillary (CM), lymphatic (LM), venous (VM) or combined) may have an impaired quality of life (QoL), due to their symptoms, which include pain, swelling, bleeding, thrombosis, and functional impairment. Unfortunately, current treatment methods are challenging and not always successful. Previous studies have shown that the mTOR-inhibitor sirolimus is an effective treatment for these patients. Target levels of 10–15 ng/ml were well tolerated; however, grade three adverse events were observed (ranged 20–40%).
Methods
A pilot study was performed using a Challenge–Dechallenge–Rechallenge (CDR) design to determine the pharmacodynamics of low target levels of sirolimus (target levels 4–10 ng/ml) in respect of efficacy and adverse events in patients with disabling low-flow vascular malformations without treatment alternatives. The patients received sirolimus over a three-to-six-month period (Challenge), followed by the withdrawal of sirolimus (Dechallenge). If the complaints returned, sirolimus was reintroduced during a twelve month period (Rechallenge). Efficacy was determined on pain (end point of the pilot study) and other symptoms related to the vascular malformation; and adverse events were determined in all phases of the study.
Results
An improvement in symptoms was seen in 92% (n = 11/12) of patients during the Challenge phase. In the Rechallenge phase, a positive response rate of 78% was found (n = 7/9). These response rates are comparable to those found in the literature despite low target levels of sirolimus. However, less serious adverse events were observed with low dose sirolimus, especially bone marrow toxicity and grade III liver toxicity.
Conclusions
This pilot using low dose sirolimus showed high efficacy in patients with therapy resistant and disabling low-flow malformation, with a lower incidence of serious adverse events (especially bone marrow toxicity and grade III liver toxicity). This is extremely relevant to patients with low-flow vascular malformation, as current clinical protocols tend to advise lifelong treatment.
Trial registration
The pilot study was part of a phase III study. Trial registration: EudraCT number: 2016-002157-38 and ClinicalTrials.gov Identifier: NCT03987152, registered 06/14/2019 - Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03987152?term=sirolimus&cond=Vascular+Malformations&cntry=NL&draw=2&rank=1
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