NOTCH1 and cancer: We thus implemented patient-derived xenografts from metastatic samples of human ccRCC to explore its clinical significance.<h4>Results</h4>We showed that pL1575P NOTCH1 mutation was an activating mutation, leading to the expression of NOTCH1-intracellular domain-active fragments in both cancer cells and tumor endothelial cells, suggesting a trans-differentiation of cancer cells into tumor micro-vessels.