To purify ECs from lungs with metastases, we used fluorescence-activated cell sorting (FACS) to exclude cells expressing hematopoietic, epithelial, fibroblastic or cancer cell markers (CD45, CD11b, EpCAM, CD140a/b and green fluorescent protein (GFP)), and to select cells expressing the endothelial marker CD31 (Fig. 1e and Extended Data Fig. 1c). Here, PECAM1 is linked to cancer.