Metastasis is the process through which cancer cells detach from a tumor and travel the circulatory system until they reach an uninfected site on which to grow anew. It is one of the least understood mechanisms in medicine though it is the cause of nine out of every 10 deaths from cancer. Traditional research has so far yielded little headway, which is why M.I.T. is building a new institute which will pair cancer scientists with engineers to conduct research under the rubric of systems biology.