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‘Chemo brain’ and cognitive decline after cancer

Cancer and its treatments cause a variety of side effects, some of which people recover from quickly, while others last long after treatment is over. After chemotherapy, around 70% of cancer survivors…

Around 70% of cancer survivors report difficulties with memory and concentration after chemotherapy. Image from

Cancer and its treatments cause a variety of side effects, some of which people recover from quickly, while others last long after treatment is over. After chemotherapy, around 70% of cancer survivors report difficulties with memory and concentration – this is colloquially known as “chemo brain”.

But while many cancer survivors report problems with memory or concentration, few studies have found a relationship between the results of formal cognitive testing and self-reported symptoms. In fact, formal cognitive assessments of survivors often show their performance is still within the normal range.

This doesn’t mean that cognitive symptoms should be ignored. If you think something is wrong, you can undergo a formal assessment by a neuropsychologist (a psychologist who specialises in the brain), which usually involves standardised clinical neuropsychological tests – pencil-and-paper or computer-based tests that measure memory, language and perception.

Intellectual performance

Studies that evaluate cancer patients over time (longitudinal studies) have shown that about 20% to 30% have cognitive problems, whereas we would expect about 10% impairment in healthy people.

Earlier research suggested anywhere between 15% to 50% of adults with early stage cancers may have cognitive impairment after chemotherapy. But much of the research has been limited to women with a breast cancer diagnosis. And the early studies tested people once after chemotherapy, so they cannot tell us how people’s cognitive function was before chemotherapy.

Despite some variability in research results, there seems to be a group of people who experience cognitive impairment during or after cancer treatment, which may be worse after high-dose chemotherapy. And for some people it may last five to ten years or more.

While the cognitive deficit is usually mild (such as difficulty finding the right word or forgetting people’s names), it can impact people’s daily activities and may be more pronounced in specific situations such as those requiring multitasking.

What’s to blame – cancer or chemo?

Studies testing people after a cancer diagnosis show that around 30% of people with breast or colorectal (bowel) cancer will have cognitive impairment, before any chemotherapy. So simply attributing the cognitive decline on chemotherapy is not accurate, as the cancer could, in fact, be to blame.

Cognitive impairment has also been shown in some women diagnosed with breast cancer who did not undergo chemotherapy but were treated with hormonal therapies such as tamoxifen, anastrozole and letrozole.

Even before chemotherapy, some people with cancer experience problems with memory, language and judgement. Image from

The underlying causes of cognitive impairment in cancer survivors are unknown. But a number of proposed mechanisms are being investigated. These include the toxic effects from chemotherapy and/or the cancer on the brain, changes in hormonal levels, clotting or inflammation in the brain, and genetic predispositions.

Some genetic factors known to increase the risk of Alzheimer’s disease have also been implicated in causing cognitive decline after chemotherapy. But most of these studies are small and there are some conflicting results.

Multiple other genes are being investigated, including ones that influence the metabolic breakdown of dopamine, DNA repair, regulation of inflammation in the brain and the blood-brain barrier designed to protect our brain from toxic insults.

Changes in oestrogen levels due to early abrupt menopause in women treated with some chemotherapy agents were also implicated, but larger studies have not shown a strong association.

Most work evaluating the mechanisms of cognitive impairment has been done with animal models. These suggest that in rodents at least some chemotherapy agents may decrease the generation of new neurons in the hippocampal area of the brain, cause damage to white matter or small blood vessels in the brain, or interfere with the hypothalamic-pituitary axis (the hormone glands).

Future treatments

No interventions have yet proven to prevent cognitive impairment from occurring in people with cancer or to treat it once it has occurred. But our team is running a number of studies to evaluate different types of interventions.

Two of these studies are evaluating approaches to cognitive rehabilitation (retraining the brain) for those experiencing ongoing cognitive symptoms six months to five years after chemotherapy for early stage cancer: one is via a 15-week computer-based training program that can be done at home; the other is six weeks of face-to-face retraining and learning sessions.

No therapies have been shown to prevent cognitive decline in people with cancer but the research is underway. Flickr/Judy **

The third study is evaluating whether a standardised extract of the herb gingko biloba can help to prevent or decrease cognitive impairment with chemotherapy.

To test these interventions we include a control group of people in each study who don’t receive the intervention – this shows us how much improvement occurs naturally with time.

It’s hoped that these studies, as well as work we are doing in animal models, will tell us what causes cognitive problems in people with cancer, and then enable us to develop more targeted strategies for preventing or minimising cognitive impairment in cancer survivors.

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13 Comments sorted by

  1. Shaun King


    Out of all the cancer treatments, chemotherapy has the lowest "cure rate" and does the most 3rd party damage to humans.

    The question must be asked, "why is the most dangerous and barbaric cure used above all the available natural remedies?"

    and "Why are millions and millions of dollars spent (and collected) on researching the most "unlikely" cure, when likely cures go ignored?"

    I suppose, like everything involved in making a profit, you have to follow the money. Who benefits from our current barbaric cancer treatment at the expense of all the others?

    1. Mark Amey

      logged in via Facebook

      In reply to Shaun King

      Shaun, a good friend of mine was diagnosed with breast cancer, around seven years ago, around the same time as my wife. My wife pursued surgery, chemotherapy and radiotherapy. She has since had one metastasis requiring back surgery and stereotactic radiotherapy. She also receives a drug called Herceptin which inhibits the growth of her particular type of tumour. She contimues to work nd lead a relatively normal life.

      My friend, however, pursued the sorts of natural cures of which you speak. She has been dead for five and a half years, leaving two young children. This is why most of us avail ourselves of, what you regard, as a treatment with a 'low cure rate'.

      Shaun, perhaps you should abstain from commenting on health care, and stick to design!

    2. Daniel Boon

      logged in via LinkedIn

      In reply to Mark Amey

      Mark ... your comment is based on what you perceive ... factual or otherwise.

      There are natural remedies which are largely 'free' and man-made remedies that try to copy natural remedies that are expensive ... bottom line is - by design - we all die, some earlier than others ...

    3. Mark Amey

      logged in via Facebook

      In reply to Daniel Boon

      'Mark ... your comment is based on what you perceive ... factual or otherwise.'

      Thanks for the well thought out comment.

  2. Sonia Hines

    Internerd at Queensland University of Technology

    Thanks for an interesting article, Janet. Our centre did a systematic review on interventions to treat chemo-brain; hopefully the article based on the review will be coming out soon. Like you, we were unable to identify any effective therapies based on the current evidence. I'd be interested to see the results of your new studies when they're available.

  3. david menkes

    associate professor

    This is an important and interesting article. I am alarmed, however, by Shaun King's comment, which strikes me as ill-informed and possibly dangerous. Chemotherapy isn't one thing, it's a whole category of different treatments for different cancers, and cannot be dismissed so recklessly. High quality, accessible evidence should guide treatment decisions, ideally to be made jointly by clinician and patient working together.

    As for 'following the money', that's a good point, but applies to as much to unorthodox practitioners ($1000 for a vitamin C infusion anyone?) as it does to pharmaceutical companies controlling data and publishing only studies favourable to their products. Both kinds of abuse can harm patients and should be resisted.

  4. Meg Thornton


    I find myself wondering whether the researchers have accounted for the cognitive problems caused by stress. So far I'm cancer-free, but I know when I'm under periods of intense stress (such as recently when I wound up losing my home and being unable to find replacement accommodation) my cognitive function drops like a rock. It's as though I've only got a limited amount of "desk space" in my head for all the things I need to think about, and if I get a big worry dropped on me it pushes something…

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  5. Tom Hennessy


    Chemotherapy and radiation therapy cause massive oxidation.
    "Collateral Damage in Cancer Chemotherapy: Oxidative Stress in Nontargeted Tissues" "132 anticancer drugs" "Fifty-six of these have been reported to induce oxidative stress"

    "Chemotherapy-induced ROS/RNS species [and their concomitant oxidative damage to proteins (including anti-oxidant and energy-generating enzymes), lipids, nucleic acids, and larger cellular components (e.g., membranes and mitochondria)] are prime suspects in the toxic side effects of acute or chronic chemotherapeutic treatment."
    Essentially they age you.
    "Rejuvenation of antioxidant and cholinergic systems contributes to
    the effect of procyanidins extracted from the lotus seedpod ameliorating
    memory impairment in cognitively impaired aged rats"

  6. Tom Hennessy


    Lung cancer is a 'human model of cancer' in that , smoking causes cancer, accepted. Smoking causes polycythemia , 'smokers polycythemia' , proven.
    “Smoking–a major cause of polycythemia”

    Lung cancer can be caused by polycythemia .
    "Polycythaemia in lung cancer"

    Polycythemia can be caused by pollution.
    “Elevation of hemoglobin concentration through exposure to indoor air pollution”

    Polycythemia causes lung cancer , or more importantly , is indistinguishable from lung cancer.
    "Extramedullary hematopoiesis mimicking the appearance of carcinomatosis".

    Those people who 'catch' lung cancer , or other cancers , could be manifesting polycythemia induced 'cancer'.

  7. Idelle Davidson


    Dear Drs. Vardy and Dhillon,

    Thank you for this fabulous overview of the cognitive issues that affect so many of us after cancer treatment. As you may know, I write about chemo brain as well from the patient perspective and have a blog completely devoted to the topic at Please feel free to visit us there anytime where you'll find comments and articles on the latest research.

    I do have a question about your computer-based training intervention. There have been a couple of studies out recently (Von Ah and Kesler) studying groups of breast cancer survivors and outcomes using commercially available software programs. Will you be using the same type of software or have you developed your own and how will your study differ?

    With gratitude for your efforts in advancing the research,

    Idelle Davidson
    co-author, "Your Brain After Chemo: A Practical Guide to Lifting the Fog and Getting Back Your Focus."

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