WEDNESDAY, March 19, 2014 (HealthDay News) — Having radiation therapy after a mastectomy benefits patients 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. 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.

On the other hand, the risk of cancer recurrence and death in women with no cancer in their lymph nodes was unaffected by radiation therapy, according to the study, which will also be presented March 20 at the European Breast Cancer Conference in Glasgow, Scotland.

The benefits of post-mastectomy radiation were also similar “whether or not [patients] had also received chemotherapy or hormonal therapy,” said study lead author Dr. Paul McGale of the Clinical Trial Service Unit in Oxford, U.K.

He noted that, until this study, there was uncertainty about whether radiation therapy would benefit breast cancer patients with cancer that had spread to just a few lymph nodes under the arms.

“It is already accepted that women with four or more positive nodes benefit from radiotherapy after mastectomy, and these findings confirm this benefit,” McGale said in a meeting news release. “However, it is for women with between one and three positive nodes where the previous evidence has been unclear.”

The bottom line, he said, is that “women being treated today are likely also to benefit from radiotherapy if they have any positive lymph nodes.”

Two U.S. breast cancer experts said more data on the value of post-mastectomy radiation therapy has been sorely needed.

“The role of radiation therapy after mastectomy for women who have less than four lymph nodes involved by cancer has been controversial, due to a lack of sufficient evidence,” said Dr. Sheryl Green, assistant professor of radiation oncology at the Icahn School of Medicine at Mount Sinai, in New York City.

“Most current guidelines suggest that this treatment decision should be individualized based on a patients’ specific risk profile and careful consideration of both the benefits and risk of radiation therapy,” she said.

Green said the new study gives women and their doctors better guidance, but medicine has also changed since the time the trial was begun.

“Although this data suggests a benefit to radiation therapy in this group of women, we do not know if it’s directly applicable to women currently treated with more modern chemotherapy regimens, which are known to be more effective than those used in these studies,” she said.

“[Also], radiation treatment has become increasingly more targeted and can spare surrounding healthy tissues to a greater extent than was utilized in these studies,” Green added. “As such, the risks of radiation treatment are likely to be significantly lower than previously thought.”

Dr. Stephanie Bernik, chief of surgical oncology at Lenox Hill Hospital in New York City, said there has been a “need for clarification” as to whether radiation therapy might help women whose breast cancer has spread to between one and three lymph nodes.

“This study may begin to change the practices of radiation oncologists in the United States,” Bernik said. “But some may feel that a randomized prospective trial is still needed.”

More information

The U.S. National Cancer Institute has more about breast cancer treatment.