. >> reporter: instead of using just chemotherapy, doctors added two more drugs in herceptin and perjeta. when this method tested in clinical trials it expanded the patient's average life expectancy by more than a year. >> this is the kind of discovery that's unprecedented. we don't see anything like this. >> reporter: uncommon because most breakthroughs have only added a few months to life expectancy. the study also found patients given the cocktail of drugs lived nearly five years, compared to the usual life span of two to three years. >> there are women who will be treated with this therapy who will never relapse. these will be -- the disease will be controlled. in other words, incurable disease in some patients will become curable. >> reporter: both herceptin and perjeta developed at genentech. they point out the therapy isn't new to most doctors but the clinical trial showing its effectiveness is. the findings were published in the new england journal of medicine. >> the study is really the result of many years of reserve here and in fact about 30 years. in really trying to understa