Currently it is not possible to predict which individual patient will benefit from treatment with an mTOR inhibitor. A predictive biomarker for efficacy of mTOR inhibitors is urgently needed and would be helpful, as a predictive biomarker may facilitate the development of combination therapies, of individual titration of the dose, and it may facilitate early clinical studies. Furthermore, it may spare the patients unnecessary side effects. mTOR inhibitors may fail in individual patients because angiogenesis is not sufficiently inhibited. Non-invasive imaging of VEGF before and early after start of treatment may have predictive value for treatment efficacy.