Tyrosine kinase inhibitors of VEGF receptors: clinical issues and remaining questions

The number of VEGFR tyrosine kinase inhibitors (TKIs) used as an anti-cancer agent is rapidly increasing, but several issues in clinical practice remain to be elucidated. VEGFR TKIs are multikinase inhibitors that have additional targets such platelet-derived growth factor receptors, which may result in an increased efficacy as well as an increased toxicity. Efficacy in several cancers has been shown, but acquired resistance also occurs during treatment with this new class of drugs. Tumor response evaluation can be a challenge, because VEGFR TKIs can cause extensive tumor necrosis without a marked decrease in tumor size. Therefore, new response criteria and functional imaging techniques are required. In this review we will also focus on the specific toxicities and their management: hypertension, proteinuria, cardiac toxicity, fatigue, hypothyroidism, voice changes, gastrointestinal toxicity, cutaneous reactions, wound healing, hemorrhage and thromboembolic events, hematological toxicity and cerebral toxicity. Furthermore we will discuss some issues regarding the pharmacology and dosing of these drugs. This review may provide important information to clinicians who prescribe VEGFR TKIs to their patients.