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Two new studies are reviving debate over the causes of "chemo brain," a mental fog that affects up to 75% of cancer survivors.

Cancer patients for decades have complained of feeling forgetful ormentally fuzzy, with many blaming toxic chemotherapy regimens. Whilethe problem feels very real to patients, some doctors have dismissed theissue as imaginary.

Now, new research shows evidence of mental fog in women's brain scans.

A study presented last week at a meeting of the Radiological Societyof North America found that chemo can cause brain changes that affectmemory and concentration.

Researchers studied 128 breastcancer patients who complained of chemo brain, scanning their brainsboth before and after treatment, according to the study, presented byRachel Lagos, a radiology resident at the West Virginia UniversitySchool of Medicine.

Researchers used tests called PET/CTscans, or positron emission tomography, which captures brain activity bymeasuring how quickly it uses energy. CT scans, or computed tomography,use multiple X-rays to provide detailed pictures.

Lagos andher colleagues found declines in brain activity in areas involved withlong-term memory, as well as problem solving, organizing andprioritizing. "Every single person showed change," Lagos says.

About 20% of cancer survivors complain of persistent memory problems,long after treatment ends, according to the National Cancer Institute.Patients with demanding professional jobs are more likely than others tocomplain of memory problems.

Scientists so far don't know for sure what might cause these symptoms.

Doctors such as Patricia Ganz, of UCLA's Jonsson ComprehensiveCancer Center, are studying the role of inflammation both in chemo brainand cancer-related fatigue. Her research has found that many women whocomplain of mental fog also suffer fatigue, depression and sleepproblems.

A study by Tim Ahles, of New York's MemorialSloan-Kettering Cancer Center, suggested that women may be moresusceptible to chemo brain if they carry a form of a gene linked toAlzheimer's disease. It's also possible that memory problems and cancerhave common risk factors, giving patients a greater chance of both.

Reaction to Lagos' study among breast cancers survivors has beendramatic. She received 800 e-mails from cancer survivors within a day ofpresenting her findings. Many were relieved that a doctor had confirmedtheir symptoms were real, Lagos says.

"People I'd never metwhere sharing their experiences. It was heartbreaking," Lagos says. Forpatients, being told that their symptoms aren't real "can be even worsethan getting the diagnosis in the first place, because people think,'Oh, I'm crazy.'"

A small study presented today at the annualSan Antonio Breast Cancer Symposium, however, suggests that chemo maynot be to blame for the women's memory impairments.

That'sbecause women who complained of chemo brain had lower scores on memorytests even before treatment, says researcher Bernadine Cimprich, of theUniversity of Michigan School of Nursing. Her study of 99 people usedfunctional MRIs, or magnetic resonance imaging. Women diagnosed withcancer scored worse than healthy women in a comparison group, bothbefore and after patients' treatment.

Her findings areconsistent with earlier studies, which have found that 20% to 30% ofpatients have lower-than-expected scores, even before chemo.

Women who underwent chemo reported more fatigue than other women, evenbefore receiving the drugs, Cimprich say. The more exhausted womenfelt, the worse their scores.

That suggests that at least someof the women's memory problems could have been caused by the stress andsleeplessness of being diagnosed with cancer, Cimprich says.

Studies show that other cancer therapies, such as a hormonal drug calledtamoxifen, also can cause fatigue, according to the NCI.

Early menopause, which can be caused by chemotherapy or surgery toremove the ovaries, also can cause memory problems, says oncologistClaudine Isaacs, of Georgetown's Lombardi Comprehensive Cancer Center.Hot flashes caused by medications or early menopause can make women losesleep, affecting their memory.

Cancer centers might be ableto relieve women's symptoms by offering more psychological support,Cimprich says, as well as cognitive behavior therapy and mindfulnessactivities, which can include meditation. Exercise also has been shownto relieve fatigue and give people more energy.

Lagos sayswomen can also cope with their mental fog by making lists and plans. Forexample, women in an earlier study felt overwhelmed by the task oforganizing and cooking a meal.

But the same women were able tofunction much better after researchers gave them written menus, whichhelped the women focus their grocery shopping and meal preparation,Lagos say.

"It's critically important to understand the sideeffects of therapy and minimize them," Isaacs says. "We don't want womento say no to very important therapy because of this."

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