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Genetic tests for breast cancer may miss strains of disease, Pitt study finds

| Monday, Aug. 1, 2016, 9:00 p.m.
A pink ribbon used for breast cancer awareness campaigns.
A pink ribbon used for breast cancer awareness campaigns.

Genetic tests that help doctors tailor breast cancer treatment to individuals based on their genes might be missing dangerous strains of the disease in some patients, according to a new University of Pittsburgh study.

The study points to a potential pitfall in the rush to adopt precision medicine, which in cancer treatment often involves targeting genetic mutations that drive tumor growth, said Adrian Lee, one of the study's authors and a professor of pharmacology and chemical biology at the University of Pittsburgh Cancer Institute and Magee Womens Research Institute.

“We want to apply more of these tests, but we need to understand how to use them,” Lee said.

Researchers wanted to know if testing one sample from a breast tumor — the standard practice — produced different results than testing multiple samples. In 18 of 71 patients, testing multiple samples produced different results than testing one sample, according to study results.

Several subtypes of breast cancer can exist within one tumor, and some are more aggressive than others, Lee said. If single-sample testing misses aggressive types, the patient might not receive the best available treatment, he said.

The results suggest broader sampling could lead to better treatment, but it is the first study of sampling methods in genetic tests and requires more study before changes would be warranted, he said.

The Pitt researchers looked specifically in regions where they thought they were most likely to find a mix of tumor subtypes to test their principle, he said. Future studies could sample randomly to get better results.

The study also did not assess whether patients with a greater mix of breast-cancer subtypes were any more or less likely to recover, he said.

Tests on other types of cancer ­— lung, prostate or pancreatic, for example — could also help explain how the mix of cancer types affects treatment, he said.

The tests allow doctors in some cases to prescribe medicine that attacks genetic mutations more precisely and with fewer side effects than chemotherapy and radiation.

Gene-targeted treatments have been a standard part of breast-cancer treatment for about five years, Lee said. Five-year survival rates have reached 93 percent for women diagnosed at Stage 2, according to the American Cancer Society.

One of the most common genetic testing panels, Oncotype DX, has been associated with a decrease in chemotherapy use among young women, according to a study from University of Texas' MD Anderson Cancer Center.

The Pitt study points to broader questions about how differing methods in the complex new field of precision medicine can obscure how effective any given treatment is, said Spencer Hey, a research fellow at Brigham and Women's Hospital in Boston and a faculty member at the Center for Bioethics at Harvard Medical School. Hey recently published a paper in the journal Science titled “Countering Imprecision in Precision Medicine.”

The proliferation of genetic tests and their results makes it tempting to say that any given association between a gene and a sickness is significant, but the situation is often more complicated, he said.

“The gene is a shorthand for a complex process, and we need to be diligent in making it explicit how we probe that process,” he said.

Wes Venteicher is a Tribune-Review staff writer. Reach him at 412-380-5676 or wventeicher@tribweb.com.

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