Researchers led by scientists at Oxford University analyzed the combined evidence from 194 studies of more than 145,000 women with early stage breast cancer who were treated with drugs that were being tested during the 1980s.

The analysis found that combined chemotherapy and hormone therapy could cut the risk of death within 15 years of diagnosis in half. For women of any age with hormone-sensitive breast cancer — the most common type — tamoxifen therapy for five years reduced the breast cancer death rate over the next 15 years by about one-third.

The review is the fourth analysis to be conducted by the same group of scientists on the largest database of patients for any type of cancer. Earlier analyses measured the effect of various drugs on recurrence and survival over five and 10 years. The last overview, in 2000, found that improved treatments over the preceding decade had reduced breast cancer death rates by up to 25 percent among some groups in Britain and the United States.

About 1.15 million new cases of breast cancer are diagnosed every year worldwide.