Just about anyone who's had any experience with cancer knows that chemotherapy can cause some unpleasant side effects. Nausea, fatigue, and hair loss are all common complaints.

Over the past few years, though, a lesser-known side effect -- the cognitive dysfunction commonly called "chemo-brain" -- has been getting more attention from patients and doctors.

"We have increasing numbers of long-term cancer survivors who are trying to get back to a normal routine, and that's where you begin to notice things like cognitive side effects of chemotherapy," said Tim Ahles, PhD, who gave a presentation on the problem at a recent survivorship conference sponsored by the American Cancer Society.

People who have chemo-brain may find themselves unable to concentrate on their work, or unable to juggle multiple tasks. Some find they don't remember things as well as they used to.

"The impact on the individual really depends to a large extent on what kind of demands they have at work or in life in general," said Ahles, a professor of psychiatry at Dartmouth Medical School and director of the school's Center for Psycho-Oncology Research. "People who have very demanding or stressful jobs, or have to multitask and need high cognition, those people are going to notice subtle shifts."

Subtle or not, chemo-brain is frustrating to patients, who may suddenly find themselves unable to accomplish tasks they formerly completed with ease. And it's a mystery to doctors, who are still trying to understand what causes it and who is likely to suffer.

But researchers are making progress, and new studies have yielded more insights.

In the past, Ahles said, doctors assumed chemo-brain was merely a byproduct of other chemotherapy side effects like anemia, fatigue, or depression. All of these have the potential to cause problems like memory lapses and concentration difficulties. Treating them, though, can often resolve the problem.

The real riddle, Ahles said, is how to help those patients whose chemo-brain isn't caused by one of these factors. As many as 20%-25% of patients fall into this category, but as yet there's no way to predict which patients might be affected.

One reason for this uncertainty is the methods used in previous studies of chemo-brain. In most, the patients weren't given tests to measure their mental function before they received chemotherapy. Without this baseline, judging the severity of chemotherapy-related mental decline is difficult. Newer studies, though, are taking measures of mental abilities before treatment and after; those results should help researchers narrow the field of potential chemo-brain sufferers.

Researchers are also studying whether certain genetic or hormonal factors may make some people more susceptible to mental effects from chemotherapy. Estrogen and a gene linked to Alzheimer's disease are two targets of investigation.

Another pressing issue, Ahles said, is which chemotherapy drugs cause problems, and how. Researchers are using MRI technology to identify what parts of the brain are affected by chemotherapy.

"Without knowing what the mechanism is, it's hard to develop a more targeted treatment," said Ahles. "If we knew the path, we could develop ways to prevent [the condition], or at least find ways to treat it if it did occur."

Until such answers are found, what's a patient to do? Talking to a doctor is imperative, Ahles said. A doctor can look for the most obvious causes of chemo-brain and treat them, if possible.

If that doesn't work, there are strategies that may help people deal with their chemo-brain. In a workshop held last year, breast cancer survivors described methods that had helped them function more effectively (Journal of Clinical Oncology, Vol. 22, No. 11: 2233-2239).

Many women decreased their workload and tried to avoid multiple tasks. They made lists to help themselves remember what needed to be done. They got more sleep. And they tried to avoid emergency situations where quick thinking might be required.

Patients must also remember that most people do eventually recover fully from the effects of chemotherapy, Ahles said.

"Lots of people have cognitive problems during chemotherapy, but there is a recovery process that goes on with time," he said. "A lot happens over 6 months, more over 1 year, and some after 2 years.

"For a given individual, chances are that their cognitive function will recover to normal or near-normal levels a year or two after chemo."