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Chemo Brain
This information is about adults with cancer. To learn more about the effects of cancer treatments in children (including brain problems), see our document called Childhood Cancer: Late Effects of Cancer Treatment.
For years people with cancer have worried about, joked about, and been frustrated by the mental cloudiness they sometimes notice before, during, and after cancer treatment. Even though its exact cause isn't always known, and it can happen at any time during cancer, this mental fog is commonly called chemo brain. Patients have been aware of this problem for some time, but only recently have studies been done that could help to explain it.
Doctors have known for years that radiation treatment to the brain can cause thinking and memory problems. Recently, they have found that chemotherapy is linked to some of the same kinds of problems. (To read more about radiation and its effects, see Understanding Radiation Therapy: A Guide for Patients and Families.) Research shows that some cancer drugs can cause certain kinds of changes in the brain. But it also shows that chemo and radiation aren't the only things that can cause thinking and memory problems in people with cancer.
Though the brain usually recovers over time, the sometimes vague yet distressing mental changes cancer patients notice are real, not imagined. They might last a short time, or they might go on for years. These changes can make people unable to go back to their school, work, or social activities, or make it so that it takes a lot of mental effort to do so. Chemo brain affects everyday life for many people, and more research is needed to help prevent and cope with it.
What is chemo brain?
Here are just a few examples of what patients call chemo brain:
Forgetting things that they usually have no trouble recalling (memory lapses)
Trouble concentrating (they can't focus on what they're doing, have a short attention span, may "space out")
Trouble remembering details like names, dates, and sometimes larger events
Trouble multi-tasking, like answering the phone while cooking, without losing track of one task (they are less able to do more than one thing at a time)
Taking longer to finish things (disorganized, slower thinking and processing)
Trouble remembering common words (unable to find the right words to finish a sentence)
Doctors and researchers call chemo brain many things, such as chemotherapy-induced cognitive dysfunction/impairment, cancer-therapy associated cognitive change, or post-chemotherapy cognitive impairment. Most define it as a decrease in mental "sharpness" - being unable to remember certain things and having trouble finishing tasks or learning new skills. Some doctors call it chemo brain only if it doesn't go away or get better over time. How long it lasts is a major factor in how much it affects a person's life. When it starts, how long it lasts, and how much trouble it causes can vary a lot. So the term "chemo brain" is not completely accurate. Still, it's what most people call it right now.
For most people, brain effects happen quickly and only last a short time. Others have long-term mental changes. Usually the changes that patients notice are very subtle, and others around them might not even notice any changes at all. Still, the people who are having problems are well aware of the differences in their thinking. Many people don't tell their cancer care team about this problem until it affects their everyday life.
For someone who has lost some brain function, even short-term problems with thinking and memory can be scary. Some people may have trouble remembering simple things, like closing doors or turning off lights. Others may notice that their brain doesn't work as quickly as it used to. These kinds of brain problems can cause trouble at work and at home. People who notice problems with their thinking may feel even more upset if their doctors blame it on aging or act like it's nothing to worry about. It's distressing to wonder if you'll ever be able to do your job again, or if you'll get lost on the way to a place you've been to dozens of times.
Brain problems are hard to study.
Clearly, we need to know more about chemo brain. But certain issues make brain problems hard to study. For instance, researchers sometimes use different tests to measure the problems with thinking and memory, so the results may not compare well with each other. Some people report changes that are so mild that their brain tests look normal and doctors don't have a good way to measure the changes. One study even noted that changes like this are reported by people with cancer who didn't get chemo. This may mean the tests used in the study weren't sensitive enough to pick up smaller changes. It also suggests that something other than chemo might have caused the problems. Still, chemo is one of the causes of brain problems in some people with cancer. Many of these people have brain function problems that are directly related to cancer or its treatment, and most of these problems do show up on testing.
There are also differences in when certain kinds of brain problems happen. Some researchers have tested brain function a few weeks after treatment, others months or even years later. If the problem only lasts a few weeks with no long-term changes, late testing can miss it. If the changes last more than a year but the testing stops after 6 months, no one knows how long they last. Beyond the chemo brain symptoms that start during and just after treatment, it's clear that there are some cases where brain symptoms start and even get worse after treatment is over. Many cancer treatments, including certain kinds of chemo and radiation, can cause short-term, long-term, and delayed problems.
Another timing problem in studying chemo brain is that most studies didn't test the patients before treatment to compare to results after treatment. In studies that did tests before treatment, some people were seen to have brain function problems before treatment was even started. So it's possible that the cancer itself causes some of the problems, or that some other related problem caused brain function to decline. Studies are needed that test people before the treatment and then follow up to look for changes over time.
Differences in how chemo brain is defined can also make it hard to get a handle on how often it happens. There's a wide range of estimates of how many people get chemo brain. One expert noted that, among people who get chemo, between 15% and 70% have brain problems. Another expert put the upper limit of the range at 50%. So based on these numbers, the risk of chemo brain (for people who get chemo) can be higher than 1 out of 2 or as low as 1 in 6. This may not take into account people with brain or thinking problems that may be caused by the cancer, radiation, or other causes.
What causes brain problems during cancer treatment?
Studies suggest that there may be more than one cause of chemo brain, especially for the short-term symptoms. Some people with cancer have very real brain problems even though they have not had chemo. Still others notice problems when getting hormone treatments, such as estrogen blockers or androgen deprivation therapy (treatments to lower testosterone levels). For some, problems start after surgery. Along with chemo, many different things can worsen brain function.
For instance, brain function problems could be caused or worsened by any one or any combination of these factors:
The cancer itself
Other drugs used as part of treatment, such as steroids, anti-nausea, drugs used during surgery (anesthesia), or pain medicines
Low blood counts
Sleep problems
Infection
Tiredness (fatigue)
Hormone changes or hormone treatments
Other illnesses, such as diabetes or high blood pressure
Nutritional deficiencies
Patient age
Depression
Stress, anxiety, worry, or other emotional pressure
Most of these cause short-term problems, and get better as the underlying problem is treated or goes away. A few, such as depression, can cause long-lasting brain problems unless the cause is treated.
So far, there is no known way to prevent chemo brain. For some people, treating their cancer will mean trouble with thinking, memory, planning, and finding the right words.
Studies of brain problems related to cancer and its treatment
Imaging tests have shown that in some patients, the parts of the brain that deal with memory, planning, putting thoughts into action, monitoring thought processes and behavior, and inhibition are smaller and/or less active after chemotherapy.
In some studies, these changes were more common in those who got high-dose chemo (such as chemo used for stem cell or bone marrow transplant). But a 2009 study of people who were tested before stem cell transplant noted that some problems had started before the transplant was done. (Memory greatly improved over the next 18 months, but some still had trouble with slower reaction times and fine muscle coordination.) In another series of studies, brain problems that were present 2 years after treatment were much better 4 years after treatment.
A 2011 study looked at patients who had a stem cell transplant from another person, which involves both high-dose chemo and immune-suppressing drugs. The researchers tested these patients early then observed them for 5 years after the transplant. Although their thinking problems had improved after a year, more than 40% still had mild brain problems after 5 years. The patients had improved in all other areas tested, but they were still somewhat low on hand speed and dexterity as well as word recall.
Pictures of the brain have shown lower resting brain activity in breast cancer survivors treated with chemo when compared with those who were not treated with chemo. These changes were still seen on scans of some women 5 to 10 years after treatment stopped. And during memory testing, these women had to call on and use larger areas of their brains than women who had not gotten chemo.
It's not all related to chemo and radiation, though. A small 2012 study looked at women after breast cancer surgery, before any other treatment was given. When tested, about 1 in 4 showed problems with word skills and about 1 in 7 had memory issues. Although surgery, surgical drugs, or other factors may have had some effect, the women who reported worse brain problems also reported higher stress levels.
In people with brain problems, tests of memory usually show the person is slow to learn new things, and they take longer to recall what they know. Response or reaction times slow down; attention and concentration often suffer. Most often, tests find that the person with chemo brain has more trouble in using recalled information (executive function), and in using language.
More studies are being done to try to better understand chemo brain. What's known for sure is that brain slowdown is a real problem that affects both men and women. Most of these people will notice that the problems get better over time. But others will have to learn ways to deal with brain problems that don't go away.
