Young women with breast cancer who get a mastectomy followed by chemotherapy may live longer if they also get radiation therapy as part of their treatment. So say researchers from McGill University Health Center in Montreal, who followed the progress of 318 women with high-risk breast cancer for 20 years. ("High-risk" breast cancer is cancer that is more likely to return after being treated.)

None of the women had gone through menopause at the time of treatment. All of them had breast cancer that had spread to their lymph nodes, and all had a mastectomy followed by chemotherapy. But 164 of them also had radiation treatments.

In an earlier study, the researchers had noted that the women who had radiation had fewer recurrences of their cancer and were less likely to die of breast cancer than the women who had only chemotherapy after mastectomy. But they weren't able to say for sure if radiation therapy actually helped these women live longer. But now they are prepared to say just that.

About 47% of the women who had radiation treatments were still alive 20 years later, compared to 37% of the women who had only chemotherapy. The findings were published in the Journal of the National Cancer Institute (Vol. 97, No. 2: 116-126).

Radiation has not been a standard part of treatment in this group of breast cancer patients -- younger women with high-risk cancer -- because earlier studies suggested it would not help them live longer, and because older radiation techniques tended to damage the heart.

In this study, however, heart damage did not appear to be a common problem. Three women in the radiation group and one in the chemotherapy-only group died of heart problems during the study.

Women in the radiation group did have more cases of arm swelling, which was treatable, and some scarring in the lungs. But deaths from causes other than breast cancer were not significantly different between the two groups.

These good results suggest that many women with high-risk breast cancer would benefit from adding radiation to their treatment, the researchers write.

They note, though, that there are still some unanswered questions about how best to incorporate radiation into treatment.

For one thing, the chemotherapy used in this study is not commonly used anymore. It has been replaced by newer drugs that are better at killing the cancer cells, but also have the potential to damage the heart. Although modern radiation techniques minimize damage to the heart, it is not known how combining radiation with these more powerful drugs might affect heart health. The benefits of treatment (better survival of breast cancer) might not outweigh the risks (greater chance of heart problems).

It's also not certain that women with only a few cancerous lymph nodes would get the same benefit from radiation as women whose cancer has spread to many lymph nodes. The researchers didn't find any differences when they analyzed outcomes according to how many lymph nodes were affected. But other experts who wrote an editorial about the research say the study might have been too small to detect such differences.

Both groups of researchers agree that more studies are needed using newer drugs and newer radiation techniques to know for sure which women might benefit from this treatment.