Holy crap this is amazing...once a cancer has metasised - meaning it has entered the blood stream - it can travel to other parts of the body and setup shop. The goal of a cancer cell is to proliferate as fast as possible, this require a specific environment, ie food supply and supporting tissue. This article talks about mapping where the cancer could travel to by following an envoy, which is sent out by the cancer to prepare the new site of infection. If researchers are able to map this out it could defiantly help with providing earlier detection and care for patients who have reoccurring cancers, especially breast cancer patients who are most likely to have the cancer come back.