A recent article in Forbes magazine discussed Dr. Larry Norton's theories regarding cancer metastasis and "dose-dense" chemotherapy treatment. Dr. Norton is a leading breast cancer researcher at Memorial Sloan Kettering's cancer center.
A number of scientists continue to work on theories of cancer metastasis that use mathematical modeling in determining the cycle of how tumors "seed" distant metastasis and even "re-seed" the original tumor site. Dr. Norton and others have used this knowledge to conduct research on the timing and dose of administering chemotherapy for more effective results.
There's a lot more in the article, its a good read.