Many women who are treated for breast cancer recover and go on with their lives. But for some reason, others get worse despite treatment, and they eventually die from the disease. For years, researchers have been trying to account for the differences between those treatment outcomes.

Now, new research from Princeton University has yielded some genetic clues. Professor Yibin Kang looked at the DNA in tumor samples from thousands of women with breast cancer. He used a technology called DNA microarray to look at more than 20 thousand genes in the cells of tumor samples and used powerful computers to analyze all the data from the tumor cells.

Kang and his colleagues found one gene in the DNA of tumor cells that was more active in women who had aggressive breast cancer than in women who didn't. Kang calls the gene Metadherin. He says it's present in everyone, but in 30 to 40 percent of the women in his sample, it had been "turned on."

"When it's turned on, it causes two things," Kang says. "It causes the tumor to become less sensitive to chemotherapy, and secondly, it also causes tumor to be more capable to spreading to other organs such as the lung, the bone and liver. And then eventually kill the patients."

Kang says one important question that still needs to be answered is why this gene gets turned on in some women and not others and when it becomes activated.

"We need to figure out how this gene works in great detail, because we have to know that to be able to stop its function very effectively," Kang says.

"The first thing we can do is?develop a detection kit to help the doctors to identify high-risk patients, the patients [who] are likely to have recurrence and metastasis.

"And this is very important information, because doctors can then use that information to treat those patients more aggressively, with high doses of chemotherapy and also follow them more closely."

In addition, Kang says that in the future, the protein created by the Metadherin gene could be a target for medications to make breast cancer tumors less aggressive. 

His research is published in the journal Cancer Cell.