Immune test predicts tolerance for radiation. (Radiation Therapy).

A new blood test can foretell which cancer patients are likely to suffer serious delayed side effects from radiation therapy. Physicians could use the technique to decide whom not to treat with radiation, says Nigel Crompton of Cornerstone University in Grand Rapids, Mich.

Radiation therapy is an important treatment for many cancers, but in some people it causes serious delayed side effects, after it's too late to adjust the amount of radiation used. To see whether it's possible to predict the likelihood of side effects for an individual, Crompton and his colleagues drew blood from nearly 400 people who had been diagnosed with various forms of cancer and who were about to begin long-term radiation therapy.

The researchers irradiated the blood samples with X rays and over the next 48 hours measured the proportion of certain types of immune cells that died. Such cell death is part of a healthy response to radiation damage, says Crompton. The scientists then followed the volunteers' health for an average of 29 months and gathered data on which patients developed late reactions to radiation therapy.

Six percent of the volunteers had severe delayed reactions, including problems of the skin, bladder, and intestine. Those volunteers were much more likely than the others to have had a relatively small proportion of immune cells die in the original blood test, Crompton reports.--B.H.