The new study is the largest of its kind ever conducted, and some experts are calling it a major step forward.
"It's going to give us a lot of information that we're going to use to understand cancer better and design better cancer treatments," said Dr. Larry Norton of Memorial Sloan Kettering Cancer Center.
The analysis confirmed earlier findings that there are four major classes of the disease. One type of breast cancer may be vulnerable to drugs already in use against ovarian cancer, scientists say.
The study, which was published online Sunday by the journal Nature, is the latest example of research into the biological details of tumors.
"With this study, we're one giant step closer to understanding the genetic origins of the four major subtypes of breast cancer," Dr. Matthew Ellis of the Washington University School of Medicine said in a statement. "Now we can investigate which drugs work best for patients based on the genetic profiles of their tumors."
Scientists looked at the DNA of tumors from 825 patients. Of the four main classes, one showed similarities to ovarian cancers, suggesting it may be driven by similar biological developments.
"I find this study very exciting but it really is a stay-tuned situation," said ABC's Chief Health and Medical Editor Dr. Richard Besser. "It's going to be years before this really impacts patients who have cancer."
The Associated Press contributed to this report.