Cancers that spread, or metastasize, to the brain but originate in other parts of the body outnumber those that begin in the brain by about 10 to one, making them by far the most common malignant cancer of the central nervous system. But scientists have been unclear on how cancers actually migrate to the brain — until now. A study out of Oxford University has found that cancer cells actually appear to creep along the brain's blood vessels, allowing them to infiltrate the brain sneakily and silently.

In essence, the blood vessels provide the "soil" upon which the cancer cells can grow.

The research team looked at many cancer cell types — breast, lymphatic, melanoma — in mice and humans, and studied just how these cancer cells were infiltrating the brain. They found that cancer cells were essentially "co−opting" the brain's network of blood vessels, rather than growing on the nerve cells themselves. This way, say the researchers, cancer cells are able to get all the oxygen and nutrients they need, without initially having to grow their own vascular networks to survive. In essence, the blood vessels provide the "soil" upon which the cancer cells can grow.

"Metastasis to the brain is essentially terminal, and very little is known about the process by which it occurs," says W. Shawn Carbonell, post-doctoral researchers and study author. "But by quickly remedying our lack of knowledge, we hope to be able to come up with new and better ways of treating such cancer."

The team also discovered the mechanism by which cancer cells are able to "stick" to blood vessel walls, which they say will be useful in designing anti-cancer drugs in the near future. The cancer cells possess a protein called an "integrin" on their outer surfaces, which allows them to attach themselves to the blood vessels' cell walls. When the researchers removed the integrin protein from cancer cells, the cells were unable to stick — and therefore grow — on blood vessel walls.

The study presents some exciting results, in an area in which still too little is known. Says lead author Ruth Muschel, "[o]ur research describes a novel mechanism which explains how tumour cells metastasize to the brain. The dependency of early brain metastases on the host blood vessels might provide a target for new drug therapies."

The study was published in the June 10, 2009 issue of the Journal PLoS One.