5. Needle-free electronically-controlled jet injector treatment with bleomycin is efficacious and well-tolerated in patients with severe keloids: results of a randomized, double-blind, placebo-controlled trial. 117 5. INTRODUCTION Keloids are abnormally healing scars, which are associated with a substantially reduced quality of life due to pain, itching, and restriction of movement.1,2 Keloids are most common in Fitzpatrick skins types 4-6 and are more prevalent in the African and Asian populations (prevalence of 5-10%), while Fitzpatrick skins types 1-3 are less frequently affected (prevalence of < 0.1%).3 Recent studies suggest that a dysregulated transforming growth factor beta 1 (TGF-β1) pathway contributes to keloid formation by inducing neovascularization and the formation of abnormal fibrosis.4 Neoangiogenesis and an increased activation and proliferation of fibroblasts, lead to increased collagen deposits, which plays an important role in keloid formation.5 Severely affected keloid patients are defined as having a single keloid exceeding a surface area of 10 cm2 and/or multiple keloids.6 Various factors, including Fitzpatrick skin type, anatomical location- and lesion duration may play a role in developing severe keloids.7-9 Also, external factors such as low income and severe manipulation of keloids have been associated with the development of more severe keloids.10 The first-line treatment for keloids consists of conventional intralesional needle injections with corticosteroids.11 Other treatment options include cryotherapy, intralesional 5fluorouracil (5-FU) injections and (non-)ablative laser treatments.12,13 However, drug delivery techniques as conventional needle-injections and laser treatment can be painful. Moreover, corticosteroids and 5-FU often lead to adverse effects and treatment failure.14 Therefore, alternative treatment options are urgently needed. Bleomycin, an antineoplastic agent, is a second-line option for intralesional keloid treatment. Its mechanism of action comprises delaying the cell cycle in the G2-phase, inhibition of DNA and RNA synthesis, apoptosis of fibroblasts, and suppression of collagen production.16,17 Moreover, bleomycin induces endothelial cell damage by inhibiting cytokines including TGF-β1, resulting in a reduction of the perfusion of keloids.18
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