The method involves studying drugs in small groups of people and using advanced statistical techniques to analyze the results as they come in, CBS News reports.

Anastrozole reduces breast cancer chance by 53 percent, study says.

The study, called I-SPY 2, puts small groups of women on experimental drugs or combinations, then gives them surgery to see what effect the medicines had.  

Each patient's results are analyzed as they come in, and advanced statistical methods are used to calculate probabilities that the drug would help in various situations, depending on which women had a complete response.

When enough evidence indicates a high probability of success, the drug "graduates" to final-phase testing.

On Friday, Dr. Hope Rugo of the University of California, San Francisco, gave results on veliparib, the first of seven drugs being tested. It is in a new class of experimental medicines called PARP inhibitors, which target an enzyme cancer relies on to grow.

The I-SPY 2 testing suggests that adding the chemotherapy drug carboplatin and veliparib to usual chemo before surgery improved outcomes for women with "triple negative" breast cancer - tumors that are not fueled by estrogen, progesterone or the gene that the medicine Herceptin targets.

Up to 20 percent of breast cancers are this type, and they are more common in young women, blacks and Hispanics, and women with certain breast cancer gene mutations.

Researchers were able to determine the drug's potential after tests in only 71 women and just six months of treatment. They calculated that tests of only 300 women with triple negative tumors are needed to give a definitive answer, and that the drug has at least a 90 percent probability of success in such patients. If more types of cancer are included, the probability of success drops to 55 percent.