Breast Cancer: Not One Disease but 10, Researchers Say

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In a wide-ranging new study, researchers have classified breast cancer into 10 different subtypes — a finding that could change the future of breast cancer diagnoses, treatment and survival.

The research team known as the Molecular Taxonomy of Breast Cancer International Consortium (METABRIC) analyzed the genetic makeup of 997 breast tumors from nearly 2,000 women from the U.K. and Canada who were diagnosed five to 10 years ago. The researchers extensively monitored the genetic details of the tumor samples — looking not only at gene mutations, but also at their specific activity — and compared the findings to the women’s age at diagnosis and their long-term survival rates.

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By the end of the study, which took some five years to complete, the researchers had identified 10 classifications of tumors, based on their genetic fingerprints. The researchers then confirmed the validity of those categories by testing them in a separate group of 995 breast cancer tumors.

The new categories range from very treatable to extremely aggressive, the Los Angeles Times reports. While much further study is needed to figure out whether the classification system will benefit patients with cancer in the real world, the new findings are a remarkable step forward in the understanding of how breast cancer develops and progresses.

Doctors already categorize breast tumors into a few different subgroups and adjust treatment accordingly. For example, tumors that test positive for estrogen receptors typically respond well to the drug tamoxifen, while those that have HER2 receptors can usually be treated successfully with Herceptin. Still, in many cases, doctors are at a loss to understand why some women respond to treatment and others don’t, even if they both have the same general type of tumor.

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Because patient responses can’t be precisely predicted, it can lead to overtreatment, with doctors trying therapies even though the patient may not benefit. Having a more detailed system of tumor categories can not only help avoid that problem, but also tailor treatment to individual patients and predict women’s survival more accurately. The Los Angeles Times reports:

For example, they found that tumors in two of the categories had very few DNA aberrations compared with those in other groups. Tumors in one of these categories were particularly vulnerable to immune system cells, and they had one of the best profiles for prognosis.

“These tumors do have something different about them,” Caldas said. And by studying them further, he suggested, researchers may discover that they respond well to novel treatments.

“Our results will pave the way for doctors in the future to diagnose the type of breast cancer a woman has, the types of drugs that will work and those that won’t, in a much more precise way than is currently possible,” Dr. Caldas said in a London press conference, the BBC reports.

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It will likely take at least three to five years of further study before doctors and patients can start benefiting from the new tumor classifications.

The study was published Wednesday in the journal Nature.

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