Update: New research sheds li... Health Article
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Many people undergoing chemotherapy complain of problems with memory, attention, and concentration — a phenomenon called "chemobrain" or "chemo fog." When we first wrote about chemobrain in October 2002, most of what was known of it came from the anecdotal reports of patients, often breast cancer survivors, and a few studies linking chemotherapy (but not surgery or radiation) to cognitive problems.
Researchers suggested potential explanations, including the sudden chemotherapy-induced onset of menopause, multiple medications — perhaps in combination with age-related changes in the brain — or brain damage from high doses of chemotherapy drugs. Subsequent research has shown that not all chemotherapy recipients have trouble with mental function, but for those who do, the effect can last several years. Thus far, a physiological explanation for chemotherapy-related cognitive trouble has remained elusive. But two studies may help fill in the gap.
Japanese researchers used magnetic resonance imaging to show that cancer drugs can cause temporary shrinkage in brain structures involved in cognition and awareness (Cancer, Jan. 1, 2007). The brain imaging was performed on three groups of women: breast cancer survivors who had received chemotherapy, breast cancer survivors who had not undergone chemotherapy, and a healthy control group. Compared to the other women, the chemotherapy recipients had less white matter (information-transmitting cells) and gray matter (information-processing cells) in regions of the brain involved in attention, planning, judgment, remembering, and self-awareness. Shrinkage in these areas correlated with generally lower scores on measures of attention, concentration, and visual memory. The encouraging news for women receiving chemotherapy is that within three years, follow-up scans showed no differences among the three groups.
The second study, by scientists at the University of Rochester Medical Center, found that three cancer drugs (cisplatin, carmustine, and cytosine arabinoside) used for a range of cancers tend to be more toxic to healthy brain cells than to cancer cells (Journal of Biology, Nov. 30, 2006) — at least in laboratory cell cultures. In the lab setting, these drugs killed 70%–100% of brain cells — but only 40%–80% of cancer cells. Animal studies showed that such effects lasted for at least six weeks after treatment. The drugs harmed various types of cells, including neurons that contribute to signal transmission in the brain.
The University of Rochester team speculates that these cancer drugs may block new cell formation in the hippocampus, a brain structure essential to memory and learning. The researchers stress that no one should avoid chemotherapy because of these preliminary results. But they suggest that their findings offer a physiological explanation for chemobrain and could eventually lead to ways of protecting the brain during chemotherapy.