By Liz Szabo
November 29, 2006
Doctors once dismissed complaints of "chemobrain," a common side effect of cancer therapy in which patients experience memory problems or mental fuzziness.
Research now shows that chemotherapy can cause real changes in the brain, ranging from forgetfulness to seizures, vision loss and even dementia. More than 80% of cancer patients develop memory and concentration problems, according to a study in June from the University of Rochester Medical Center in New York.
In a paper in today's Journal of Biology, scientists found that even low levels of chemotherapy can kill brain cells. The study showed that cancer drugs were even more toxic to healthy cells than to malignant ones, says Mark Noble, a professor at the University of Rochester Medical Center.
Noble tested three common chemo drugs - cisplatin, cytarabine and carmustine - on rats and in human cells in lab dishes. Chemo killed 40% to 80% of cancer cells, but 70% to 100% of healthy brain cells. Some of the normal cells continued to die for several weeks after treatment, according to the study, funded by the National Institutes of Health and the James P. Wilmot Foundation.
Significantly, chemo killed not just rapidly dividing cells - the typical target of cancer therapy - but brain cells that weren't reproducing, including those responsible for creating the insulation around nerve cells, Noble says. This insulation is important because it helps nerve signals travel quickly.
Other recent studies also document chemo's effects on the brain.
In a study to be published in January in Cancer, researchers studying breast cancer patients found that chemo may temporarily shrink certain brain areas. And in a small study published last month in Breast Cancer Research and Treatment, Daniel Silverman of the University of California-Los Angeles found that women with chemobrain symptoms had changes in the functioning of their brain's frontal cortex.
Silverman, head of UCLA's neuronuclear imaging section, says Noble's paper doesn't definitively prove that killing brain cells causes cognitive problems. He says something else may actually cause chemobrain. To really prove the connection between chemobrain and cell death, Silverman says, researchers should repeat the experiments, but also test the lab rats to see if those who lost brain cells have more trouble than others on intelligence tests.
But Patricia Duffner, a professor at the Hunter James Kelly Research Institute at the University of Buffalo, says Noble's study is "likely to act as a wake-up call." Doctors have long recognized that radiation can damage the brain, says Duffner, who wrote a review accompanying Noble's article. She says researchers should look more closely at ways to protect the brain from chemotherapy.
"It was imperative to define the problem," Noble says. "Now it is imperative to find ways to treat it."