Only those cells with the migration protein were able to break through the walls of the blood vessels.
"That's very, very valuable to be able to watch both your control and your cancer cell lines in the same environment and see how they behave as they interact with the blood system," Klemke said.
After several weeks of observation, the scientists were able to determine that the cancer cells grew something they call "false feet," thus making them more mobile, but they also needed the protein that stimulates new blood vessel formation to break through the blood vessel wall.
So it required both proteins -- one for mobility and one for generating new blood vessels -- to "complete the most critical step of metastasis, entering the blood vessels," said the university's Konstantin Stoletov, lead author of a paper on the research in a recent online edition of the Proceedings of the National Academy of Science.
If some way can be found to keep those two proteins from cooperating, the cancer could be stopped in its tracks, the researchers said.
"That would be huge because the vast majority of cancer patients succumb to the spread of the disease to other organs," Klemke said.
And once again, the zebra fish will be called into the battle. Researchers will actually be able to see how various therapeutic agents function.
"We can grow human tumor cells in an optically transparent animal so we can visualize the process in high resolution detail," Klemke said. "Then we can test the pharmaceutical agents and determine how they impact the process of tumor formation and metastasis. It's a win-win situation."
So the zebra fish, common in aquariums around the world, is likely to be on center stage for a long, long time.
Lee Dye is a former science writer for the Los Angeles Times. He now lives in Juneau, Alaska.