Podsypanina and her colleagues performed a series of experiments in mice.
First, they injected normal mammary cells that contained cancer-inducing oncogenes, which could be switched on and off. These cells migrated through the bloodstream to the lungs, residing there for four months. They did not begin to grow aggressively until the oncogenes had been turned on, but they did so without first going through the stage of being a primary tumor.
Next, they injected normal cells without manipulating any oncogenes.
"Cells that did not have any oncogenes in them and do not transform spontaneously as per all published studies, we could see little colonies of these cells when we inspected the lungs," Podsypanina said. "At no point, never, did we see a solid vision that would resemble metastatic colonies, [but] it appears that every time we looked at the animal, the colonies appeared to be larger."
When these normal ectopic cells were injected back into a new generation of mice, they developed into normal mammary glands.
"It's a beginning," Podsypanina said. "It's an important step to show whether or not the first step of the metastatic cascade is something a normal cell can accomplish."
Visit the American Cancer Society for more on oncogenes.
SOURCES: Katrina Podsypanina, M.D., Ph.D., senior research scientist, department of cancer biology and genetics, Memorial Sloan-Kettering Cancer Center, New York City; Claudine Isaacs, M.D., director, clinical breast cancer program, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, D.C.; Aug. 28, 2008, Science
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