A study finds that breast cancer patients taking the drug tamoxifen can cut their chances of having the disease come back or kill them if they stay on the pills for 10 years instead of five years as doctors recommend now.

The results could change treatment, especially for younger women. They are a surprise because earlier research suggested that taking the hormone-blocking drug for longer than five years might be harmful.

In the new study, women who took tamoxifen for 10 years lowered their risk of a recurrence by 25 percent and of dying of breast cancer by 29 percent compared to those who took the pills for just five years.

The study was discussed at a cancer conference in Texas and published in the journal Lancet.