The New York Times
In findings that are fundamentally reshaping the scientific understanding of breast cancer, researchers have identified four genetically distinct types of the cancer. And within those types, they found hallmark genetic changes that are driving many cancers.
These discoveries are expected to lead to new treatments with drugs already approved for cancers in other parts of the body and new ideas for more precise treatments aimed at genetic aberrations that now have no known treatment.
The study, published online Sunday in the journal Nature, is the first comprehensive genetic analysis of breast cancer, which kills more than 35,000 women a year in the United States. The new paper and several smaller recent studies are electrifying the field.
"This is the road map for how we might cure breast cancer in the future," said Dr. Matthew Ellis of Washington University, a researcher for the study.
Researchers and patient advocates caution that it will still take years to translate the new insights into transformative new treatments. Even within the four major types of breast cancer, individual tumors appear to be driven by their own sets of genetic changes.
The study's biggest surprise involved a particularly deadly breast cancer whose tumor cells resemble basal cells of the skin and sweat glands, which are present in the deepest layer of the skin. These breast basal cells form a scaffolding for milk duct cells.
And, the researchers report, their genetic derangements make these cancers a much closer kin of ovarian cancers than of other breast cancers. The study gives a biologic reason to try routine treatments for ovarian cancer in basal-like breast cancer, the investigators said.
Two other types of breast cancer, accounting for most cases of the disease, arise from the luminal cells that line milk ducts. These cancers have proteins on their surfaces that grab estrogen, fueling their growth. Just about everyone with estrogen-fueled cancer gets the same treatment. Some do well; others do not.
The genetic analysis divided luminal cancers into two distinct subtypes. The luminal A subtype had good prognoses while luminal B did not, suggesting that perhaps patients with luminal A tumors might do well with just hormonal therapy to block estrogen from spurring their cancers while luminal B patients might do better with chemotherapy in addition to hormonal therapy.
The fourth type of breast cancer is what the researchers called HER2-enriched. Breast cancers often have extra copies of a gene, HER2, that drives their growth.
Although the drug Herceptin is approved for every breast cancer patient whose tumor makes too much HER2, the new analysis finds that not all of these tumors are alike. The HER2-enriched should respond readily to Herceptin; the other type might not.
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