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It is believed that tumor cells can give rise to endothelial cells and tumor endothelium has a neoplastic origin. Yet, the stimuli and underlying mechanism remain unclear. Here, we demonstrate that adriamycin or paclitaxel, first-line chemotherapy agent, induced breast cancer cells to generate morphological, phenotypical and functional features of endothelial cells in vitro. In xenografts models, challenges from adriamycin or paclitaxel induced cancer cells to generate the majority of microvessels. Importantly, in breast cancer specimens from patients with neoadjuvant anthracycline-based or taxane-based chemotherapy, tumor-derived endothelial microvessels, lined by EGFR-amplified or/and TP53+-CD31+ endothelial cells, was significantly higher in patients with progressive or stable disease (PD/SD) than in those with a partial or complete response (PR/CR). Further, exposure to the Notch signaling inhibitor and gene silencing studies showed that Notch signaling inhibition or silencing Nothc4/Dll3 decreased endothelial markers and function of tumor-derived endothelial cells under chemotherapy treatment, which may be through VEGFR3. Thus, our findings demonstrate that chemotherapy induces functional tumor-derived endothelial microvessels by mediating Notch signaling and VEGF signaling, and may provide new targets for anti-angiogenesis therapy in breast cancer.