Radiation therapy after undergoing mastectomy benefits women with breast cancer that has spread to just a few lymph nodes under their arms, a new study suggests.

Researchers analyzed data from nearly 3,800 women in 14 clinical trials that started between 1964 and 1982, News Max Health reports. After their mastectomy and surgery to remove lymph nodes under the arms, the women were randomly selected to receive either no radiation therapy or radiation therapy to the chest wall and other regions.

Some of the women had no cancer in the lymph nodes, some had cancer in one to three lymph nodes, and others had cancer in four or more lymph nodes.

The women were followed for an average of just over 11 years. Radiation treatment cut the risk of cancer's return by 32 percent and the risk of dying from breast cancer by 20 percent in those women who had cancer in one to three lymph nodes, the researchers reported March 19 in the journal The Lancet.

Women with cancer in four or more lymph nodes were 21 percent less likely to have cancer recurrence and 13 percent less likely to die of breast cancer if they had undergone radiation therapy, the study found.