WHEN YU ZHANG’S CANCER PATIENTS report problems with memory, focus or decision-making, they’re often relieved to learn that the symptoms are a common side effect of both cancer and its treatment. Zhang, a medical oncologist at the West Haven VA Medical Center in Connecticut, says patients find solace in knowing their perceived brain fog isn’t all in their head. In reality, they often have a condition experienced by up to 75% of cancer patients: cancer-related cognitive impairment (CRCI).
CRCI and the colloquial terms chemo brain and brain fog describe a group of symptoms that affect memory and thinking that can be linked to cancer and its associated treatments. CRCI is a poorly understood condition that is tricky to diagnose, let alone to treat, Zhang says. In addition, many oncologists, in Zhang’s view, don’t screen for or talk to patients about the condition, which can diminish patients’ quality of life.
Zhang and other researchers anticipate that CRCI prevalence will increase as cancer treatments expand. Surgery, chemotherapy, immunotherapy, hormone therapy, radiation and targeted therapies are among the treatments that have been tied to CRCI.
To better inform oncologists—and increase patient awareness—Zhang teamed up with other physicians and scientists to develop a blueprint for validating, diagnosing and treating CRCI. Their guide was published March 5, 2025, in JCO Oncology Practice.
She recently spoke with Cancer Today about how understanding of CRCI has changed and how oncologists can better support patients.
CT: Why has CRCI been controversial?
ZHANG: Maybe 10 to 15 years ago, doctors would say, “This is not real. This is simply due to the stress of having cancer.” Or they would chalk it up to other things. But we’re starting to have more data from animal studies and imaging studies that show the brain actually changes from cancer treatment. In some of the patient studies, cognitive impairment due to cancer is independent of depression. It’s independent of other factors that we would think contribute to cognitive impairment. Now we’re starting to get more evidence that this is a real phenomenon, that this is a real syndrome that patients are experiencing.
CT: CRCI is sometimes called chemo brain. How do you feel about that term?
ZHANG: I think our correct terminology is cancer-related cognitive impairment because we’re realizing it’s not just chemo that causes these cognitive impairments in patients. Any of the treatments—and the cancer itself sometimes—can cause cognitive impairment. We’re still trying to understand the exact pathological basis, the underlying cause. There may be multiple factors that contribute to development.
CT: How is CRCI diagnosed?
ZHANG: It’s very hard to diagnose. Currently available tests for measuring cognitive impairment were designed to look at traumatic brain injury, dementia—more pathologically significant diseases.
When you screen cancer patients who are complaining of cognitive impairment, they don’t test that poorly on these neurocognitive tests, but they will report that they have significant trouble with these areas, including memory, slower processing speed, difficulty with concentration and inattention. They also report having trouble at work. Some of them are very ashamed to even bring it up because they’re afraid to talk about it. Sometimes they think it’s just them.
CT: How far into treatment might a patient start to exhibit CRCI symptoms?
ZHANG: Some patients may notice these symptoms right after the first treatment. A lot of times, cognitive impairment can be progressive. With more treatment, people may feel that their symptoms are getting worse. A lot of times, cancer-related cognitive impairment is reversible, so if you stop the treatment, the symptoms may get better or even resolve over time.
CT: What treatment options do CRCI patients have?
ZHANG: We found that exercise, yoga, mindful meditation and relaxation exercises may be helpful. After trying these activities, patients oftentimes will report their cognitive function is better.
We don’t have a good way of treating this, so we talk about compensatory strategies. We tell patients, “Try to remember to put your keys in the same place. If you have trouble planning, talk to yourself and say, ‘What am I doing? What am I supposed to do next?’ Talk yourself through the event or the thing that you’re trying to achieve. Take notes and use smartphones to remind yourself about things.” We also tell them to practice active listening, so they should summarize what’s been said to them in their own words.
CT: How has your CRCI guide been received?
ZHANG: It has been generating a lot of interest. Everyone has been very positive, and a lot of the feedback from colleagues is, “We noticed this has been going on for a long time. It’s about time that we start addressing this.”
This interview has been edited and condensed for clarity.
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