Women diagnosed with the most common form of breast cancer may benefit from staying on the drug tamoxifen for a decade instead of the customary five years. A long-awaited clinical trial published Wednesday in the journal Lancet found that staying on tamoxifen for longer lowered a patient’s risk of recurrence and of dying from breast cancer.

In the study involving nearly 13,000 breast cancer patients of all ages, European researchers found that those who were randomly given tamoxifen for 10 years had a 12 percent likelihood of dying from breast cancer over the 15-year study compared with a 15 percent risk for those who were given placebos after their first five years on tamoxifen.