The Study’s Purpose Part of a large federal project known as the Cancer Genome Atlas, the study—which was published in the science journal Nature—focused on the most common types of breast cancer and on breast cancers that hadn’t yet metastasized to other parts of the body, looking closely for genetic changes in the process. While similar studies have been published recently on lung and colon cancer, “there has never been a breast cancer genomics project on this scale,” the Atlas program director, Brad Ozenberger of the National Institutes of Health, told The New York Times.

The Landmark Findings Researchers analyzed tumors in 825 patients and found that most tumors are caused by mutations in 30 to 50 genes, leading them to identify four different types of breast cancer, each with uniquely different genetic traits: luminal A and B cancers, HER2-enriched cancers, and basal-like cancers. The latter is a relatively rare but particularly deadly strain with tumor cells that resemble the basal cells of the skin and sweat glands.

Where’s the Good News Here? There are many promising findings, and it’s hard to predict which ones will prove to be most useful in the future. One key point: in identifying the basal-like type of cancer—a type that affects 10 to 15 percent of breast cancer patients and is most common in young and African-American women—researchers found that it more closely resembles ovarian cancer and a type of lung cancer than it does other types of breast cancer. “It raises the possibility that there may be a common cause,” said Dr. James Ingle, one of 348 authors on the study.

A New Perspective on Treatment Currently, most cases of these basal-like cancers are treated with drugs called anthracyclines that can strain the heart and even cause leukemia. But now that researchers have identified a connection with ovarian and lung cancers, the less toxic chemotherapy regimen used to treat those cancers may be considered for basal-like cancers.

The study may also lead to different treatment options for HER2-enriched cancers, or breast cancers that have extra copies of the HER2 gene and tend to grow more quickly. Patients with tumors that produce extra copies of this gene are given an inhibitor, Herceptin, which effectively blocks the gene in many cases. However, the new research found that while Herceptin is used to treat every case of HER2-enriched cancer, some tumors that make too much HER2 may not respond to the drug. Researchers now know that only a clinical trial will reveal which tumors respond and which don’t—the results of which could result in greater understanding of the cancer itself and in a search for alternate treatments. "We are really getting at the roots of these cancers," said Dr. Charles Perou, the lead author on the study.

No Quick Fix While the results of the study represent major progress in breast cancer research—“a road map for how we might cure breast cancer in the future,” according to one researcher for the study—patients will have to wait years for the results of the clinical trials. Only then will scientists have more clear evidence on whether drugs that block genetic mutations can actually be used to effectively kill certain cancers.