Metastasis, when tumours spread to other organs in the body, is the leading cause of cancer-related deaths. Many extrathoracic tumours commonly metastasize to the lungs. Breast cancer lung metastases are often resistant to many types of therapy, including anti-angiogenic drugs and these patients have a poor prognosis. To investigate the mechanisms of vascularization that metastatic tumours utilize to grow and by which they develop anti-angiogenic drug resistance, we have used niche labelling and single cell RNA sequencing of endothelial cells. Vessel co-option, whereby tumour cells exploit existing blood vessels, was found to be one strategy. However, little is known about its mechanisms. Therefore, better understanding of this vascular phenotype could potentially help targeting these hijacked blood vessels for the efficient treatment of breast cancer and other lung metastases.