We demonstrate that in our in vitro model, most metastatic breast cancer cells clear a space in and appear to become part of the endothelium (without forming VE-cadherin dependent adherens junctions with the ECs), in a process we term “incorporation.” We were able to observe this process for multiple metastatic cancer lines, including MDA-MB-231 breast cancer cells, A375 melanoma cells, and SW1990 pancreatic cells. Here, CDH5 is linked to breast carcinoma.