A Duke University study has enhanced scientists' understanding of what makes breast cancer in younger women so different from breast cancer in older women.

The results provide further evidence for genetic factors as the primary contributors to young women's tumor development, which could help medical researchers develop better and more targeted therapies to treat young breast cancer patients, defined as age 45 or under.

Researchers also found that tumors in older women, defined as age 65 or above, are linked to a much wider pool of possible causes.

"Older women's cells have survived longer than younger women's cells, and in the process they have been subjected to a larger number of things that could contribute to cancer development," said Dr. Kimberly Blackwell, senior investigator for the study and breast oncologist at Duke University Medical Center. "It makes sense that there would be a more limited set of things that are contributing to young women's tumors. The result implies some influence in the younger women who develop breast cancer that hits the cells that develop the cancer harder."

This influence tends to be related to underlying genetic problems, Blackwell added.

"It could be genetic mutation from diet, nutrition, environmental exposure," she said.

The study, which was funded by the National Cancer Institute and published Thursday in the Journal of Clinical Oncology, found that the underlying difference between older and younger women's tumors was that younger women's tumors all looked pretty much the same genetically, whereas older women's were different.

"The tumors were extremely similar in both their appearance and their biology," Blackwell said, referring to the younger women's tumors. But the older women's tumors had no common genetic elements.

"It's a much more heterogeneous makeup," Blackwell said. "What this implies is a smaller set of contributors to tumor development for younger women."

After examining more than 13,000 genes each on 411 tumors, what they found were the same few hundred genes popping up over and over again in the young women's tumors.

"We were looking for which genes had a higher level of expression," Blackwell said. A gene is said to "express" itself when it is being transcribed into something called RNA, a kind of genetic Xerox. The more RNA associated with a gene, the more active the gene being transcribed.

Previous studies have shown that tumors in younger women, who represent about 15 percent of breast cancer patients, tend to be significantly more aggressive than those in women a few decades older. The younger women's cancers are faster growing and more resistant to treatment, which is one of the reasons Blackwell says it is such an important field of study.

Lalania Hall, 37, was diagnosed with breast cancer last year. For Hall, who has five sons ranging in age from 3 to 12, being a part of the study was an experience of hope. "I'm so grateful that there are people out there who are starting to focus on younger women," Hall said.

Blackwell hopes the results from her study will lead to increased scientific interest in young women with breast cancer.

"It's one of the most comprehensive studies to date," said Blackwell. "We could clearly differentiate between tumors in younger women and tumors in older women, and that is truly remarkable."

Dr. Steven Akman, an oncologist who heads the Breast Cancer Center of Excellence at Wake Forest University said that the analysis being done in the study appeared to be standard but that that did not diminish the potential utility of the results.

"The question of why younger women's breast cancers are so aggressive is a really important question that we've known about for a long time," Akman said. "What they're doing is providing a plausible biological way of looking at that question."

He added that the findings are a step in the right direction in terms of the possibility of a cure.

"It's really worthwhile work," Akman said.

"If you don't know what you're fighting against, it's almost impossible to develop a therapy for it," Blackwell said. "By isolating specific genes, we can look for specific causes and perhaps specific targetable features."