The findings, presented at the annual meeting of the American Society of Clinical Oncology in Chicago, showed that the addition of a drug known as a cyclin inhibitor increased survival rates to 70 percent, MedicalXpress rported.
The mortality rate was 29 percent less than when patients were given a placebo.
Lead author Sara Hurvitz told AFP the study focused on hormone receptor-positive breast cancer, which accounts for two-thirds of all breast cancer cases among younger women and have in the past generally been treated by therapies that block estrogen production.
"You actually can get synergy or a better response, better cancer kill, by adding one of these cell cycle inhibitors" on top of the hormone suppression, Hurvitz said.
The treatment is less toxic than traditional chemotherapy because it more selectively targets cancerous cells, blocking their ability to multiply.
The trial, which looked at more than 670 cases, included only women under the age of 59 who had advanced cancer—stage four—for which they had not received prior hormone-blocking therapy.
"These are patients who tend to be diagnosed later, at a later stage in their disease, because we don't have great screening modalities for young women," said Hurvitz.
"That's what makes us so excited, because it's a therapy that's affecting so many patients with advanced disease."
Oncologist Harold Burstein, who was not involved in the research, said it was "an important study," having established that the use of cyclin inhibitors "translates into a significant survival benefit for women."
Burstein is with the Dana-Farber Cancer Institute in Boston.
The research received funding from the Novartis pharmaceutical company.
"Hopefully, these data will enable access for this product for more women around the world, particularly in healthcare systems which assess value rigorously as part of their decisions for national access to drugs," Burstein added.