What researchers are touting as the most comprehensive analysis yet of breast cancer shows that one of the most deadly subtypes is genetically more similar to ovarian tumors than to other breast cancers.

The findings, published online this month in Nature, suggest that most "basal-like" breast tumors and ovarian tumors have similar genetic origins and potentially could be treated with the same drugs, says the study's co-leader Dr. Matthew J. Ellis, the Anheuser-Busch Chair in Medical Oncology at Washington University School of Medicine in, St. Louis.

Basal-like tumors account for about 10 percent of all breast cancers and disproportionately affect younger women and those who are African-American.

The new research is part of The Cancer Genome Atlas project, which brings together leading genetic sequencing centers, including The Genome Institute at Washington University, to identify and catalog mutations involved in many common cancers. The effort is funded by the National Institutes of Health (NIH).

"With this study, we're one giant step closer to understanding the genetic origins of the four major subtypes of breast cancer," says Ellis, who treats breast cancer patients at the Siteman Cancer Center at Barnes-Jewish Hospital and Washington University.

"Now, we can investigate which drugs work best for patients based on the genetic profiles of their tumors," he says. "For basal-like breast tumors, it's clear they are genetically more similar to ovarian tumors than to other breast cancers. Whether they can be treated the same way is an intriguing possibility that needs to be explored."

Currently, for example, basal-like breast tumors often are treated like many other breast cancers, using anthracycline-based chemotherapy. But another of Ellis's studies recently showed that women with basal-like tumors don't benefit from these drugs, which also have severe side effects. At the very least, he says, the new data indicate that clinical trials should be designed to avoid the use of these drugs in basal-like tumors.

As part of the new research, a nationwide consortium of researchers analyzed tumors from 825 women with breast cancer. The scientists used six different technologies to examine subsets of the tumors for defects in DNA, RNA (a close chemical cousin of DNA), and proteins. Nearly 350 tumors were analyzed using all six technologies.

The study confirmed the existence of four main subtypes of breast cancer: Luminal A, luminal B, HER2 and basal-like. The latter includes most triple-negative breast tumors, so-named because they lack receptors for the hormones estrogen, progesterone or human epidermal growth factor 2 (HER2). These tumors often are aggressive and don't respond to therapies that target hormone receptors or to standard chemotherapies.

"Now, we're much closer to understanding the true origins of the different types of breast cancer," Ellis says. "With this information, physicians and scientists can look at their own samples to correlate patients' tumor profiles with treatment response and overall outcomes. That's the challenge for the future — translating a patient's genetic profile into new treatment strategies."