Scientists announced Sunday that they have finished mapping virtually all of the genetic mutations in breast cancer, an effort that could soon change the way patients are treated and eventually help researchers develop better treatments.

"The catalogue of human breast cancers is nearly complete," says study co-leader Matthew Ellis of the Washington University School of Medicine in St. Louis. "It's the breast-cancer equivalent of putting a man or woman on the moon."

Among the most striking findings: One of the most lethal types of breast cancer is genetically closer to a kind of ovarian cancer than it is to other breast tumors, according to the paper, published online today in Nature.

That discovery could soon produce real benefits for breast cancer patients, Ellis says. Women with so-called basal-like breast tumors -- also known as triple-negative cancers -- would likely do better on a much less toxic chemotherapy regimen, which is currently the standard of care in ovarian cancer.

Such shifts show that doctors are beginning to change the way they look at cancers, focusing less on a tumor's organ of origin and more on the inner workings of its nucleus, down to the molecular level, Ellis says.

"Just because it's a breast cancer doesn't mean it's like every other breast cancer," says Brad Ozenberger, who oversees the research project, called The Cancer Genome Atlas, at the National Institutes of Health.

The ambitious federally funded program -- with a budget of $100 million a year -- aims to be the cancer equivalent of the Human Genome Project, which decoded and mapped the human genetic blueprint. Scientists already have published the genomes of four other cancers: brain, ovarian, colorectal and lung. In this study, scientists analyzed tissue from 348 breast cancers, finding that most tumors are caused by mutations in 30 to 50 genes, Ellis says.

The genome atlas could give drug companies ideas for new drugs that target key genetic mutations in cancer, Ozenberger says. In addition, the catalogue of genetic mistakes can also help scientists better understand how cancers develop and spread, Ozenberger says.

For example, they may discover that a newly discovered gene is involved in the immune system -- providing a clue to how cancer eludes the body's normal defenses. Already, the program has given researchers clues that both ovarian and triple-negative breast tumors could be vulnerable to drugs that block new blood vessel growth, which aim to starve tumors.

Triple-negative tumors account for about 10% to 15% of all breast cancers, and are more common among younger women and African Americans. Today, women with triple-negative tumors are treated like many other breast cancer patients, getting drugs called anthracyclines that can damage the heart and cause leukemia or a type of "pre-leukemia," called myelodysplastic syndrome, or MDS. Ellis' recent research, however, suggests anthracyclines don't help women with triple-negative tumors.

Robin Roberts, host of Good Morning America, underwent a bone-marrow transplant Thursday for MDS, caused by her successful treatment for triple-negative breast cancer in 2007. Another insight from the study: Doctors should reconsider an experimental class of drug called PARP inhibitors for triple-negative breast cancer, because early trials in ovarian cancer have been promising, Ellis says.

Breast cancer survivor Roxanne Martinez says she "choked up" when she heard that future patients might be able to skip the most toxic chemotherapies. Martinez, 32, was treated for triple-negative disease two years ago, while she was pregnant with her daughter.

While both she and her daughter are currently healthy, Martinez says anthracycline drugs made her very sick. Now, she worries about her long-term health. Martinez, of Forth Worth, says she's fascinated by the similarities between breast and ovarian cancers, which run in her family. Doctors have long known of links between breast and ovarian tumors.

One of the best known breast cancer genes, BRCA1, dramatically increases the risk both of ovarian cancer and triple-negative breast tumors. Martinez says she's thrilled that women with triple-negative tumors -- who today have the fewest treatment options -- could have better care due to this study. "Just the idea of a targeted treatment plan, that gives me so much hope," Martinez says.

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