Cognitive problems associated with the cancer treatment are subtle, particularly in memory and concentration, and many patients report difficulties while undergoing the actual treatment, said Tim Ahles, a clinical psychologist and professor at Dartmouth Medical School in New Hampshire.

But the effects appear not to be short-lived for everyone.

Ahles said patients reported trouble with things like balancing a checkbook without a calculator or reading an article an average of 10 years later, indicating it was a permanent but not worsening problem.

The mental impairment, even if subtle, can affect career and life decisions, said Ahles at an annual seminar in Tampa, Florida, sponsored by the American Cancer Society.

The issue is a concern to the growing number of cancer survivors. Currently about 8.4 million Americans alive today have a history of cancer, according to data from the National Cancer Institute. More than 1.2 million cases are expected to be diagnosed this year.

Little research has been done in the area on adult survivors of cancer compared to studies of children with cancer.

Ahles said the research on children has resulted in changes in both the way chemotherapy is delivered to the body, for example through a central line rather than directly into the spinal cord, and the schedule under which it occurs.

Further research may prove that these procedures are useful for adults, too.

"It's really something that increasing numbers of people are becoming aware about," he said.

Dr William Wood, chief of surgery at Emory University School of Medicine in Atlanta, said Ahles' research will open a new area of study into the important issue of quality of life. Patients who might expect to receive only a small benefit from chemotherapy in terms of their overall survival may opt not to have it if Ahles' findings are verified, he said.

(Agencies via Xinhua)