Part of what makes cancer so formidable is its ability to spread around the body, so that doctors can rarely be completely sure they've killed it all. But that might not be the best way to go about treating the disease after all. Now researchers at Purdue University have identified a drug that could help keep cancer contained in a dormant state – and best of all, that drug is already on the market for other purposes.

A cure for cancer is often regarded as the Holy Grail of modern medicine, but perhaps it's just as much a myth as that old cup. Instead, researchers might have more success in finding ways to keep patients in a state of long-term remission.

"Most cancer therapy is targeted with the idea that we want to kill all of the cancer cells," says Michael Wendt, lead researcher on the study. "But recently, there are lots of studies that suggest that we're never going to be able to do that. Cancer cells evolve so fast that they will always find a way to overcome any type of therapy. An emerging concept in cancer treatment is that maybe we shouldn't try to kill all of the cancer cells, but try to keep them in a low state that doesn't generate any kind of symptoms. A sort of dormancy, if you will."

The researchers say that current cancer drugs tend to target primary tumors because they're made to focus in on cells that are growing faster than normal cells. But that means they miss the metastatic cells that may be circulating through a patient's body, which can lie inactive for years at a time.

Rather than find a way to kill these rogue traveling cancer cells, the new study investigated how to keep them in that inactive state. In tests on mice with breast cancer, the team found that a drug called fostamatinib can do the trick. The drug, already approved for use in humans, inhibits a protein called spleen tyrosine kinase (SYK), which is found in these metastatic cells.

The team surgically removed the main breast tumor from the mice, and kept tabs on the tumor cells by tagging them with the bioluminescent protein luciferase. And sure enough, the technique showed promise in keeping those metastatic cells from taking hold as new cancers. The fact that fostamatinib is already approved safe for human use could help speed up the process.

"This is great for us because this is a drug with low toxicity," says Wendt. "It's designed for people with chronic disease so that they can take it for a long time. So, we think fostamatinib is a perfect candidate for this kind of years-long 'lock-'n'-block' type of approach. We think this is a good candidate to move forward for a trial to see if we can stabilize dormancy. If SYK is expressed in other cancers this could apply to those as well."

The research was published in the journal Cancer Research.