Cancer-Related Cognitive Dysfunction: When Chemotherapy Isn’t the Only Culprit - Dr M A Suboor Shaherose

For years, the term “chemo brain” has been used sometimes lightly, sometimes with real concern to describe the foggy thinking, forgetfulness, and slowed mental processing that many cancer patients report during or after chemotherapy.

While this label has helped raise awareness, it also paints a picture that’s too narrow. Because for many patients, these symptoms show up even when chemotherapy isn’t part of their treatment plan.

Cancer-related cognitive dysfunction isn’t just about chemotherapy. It’s a broader, more complex experience that can affect memory, attention, word-finding, and overall mental sharpness.

Today, oncologists are seeing more cases where patients undergoing hormone therapy, immunotherapy, or even targeted biological treatments report cognitive changes, some subtle, others more disruptive to daily life.

The science is now catching up with what patients have long been trying to explain: the mind feels different, even when the treatment doesn’t involve traditional chemotherapy.

So, what’s going on?

Take hormone therapy, for example. In breast cancer, medications like tamoxifen or aromatase inhibitors are often used to prevent recurrence. These treatments save lives, no doubt, but they also shift hormone levels that affect more than just reproductive health.

Estrogen, in particular, helps support memory, focus, and clear thinking. When it drops, some people feel foggy, find it hard to concentrate, or describe their thoughts as slow and heavy.

Immunotherapy has reshaped cancer care, bringing hope where few treatments once worked. But its effects don’t always show on scans. As it pushes the immune system to attack cancer, it can sometimes stir up quiet inflammation in healthy areas, including the brain. When this happens, patients may start noticing shifts in memory, attention, or how clearly they think—often without knowing why.

Patients may not develop full-blown encephalitis, but they might feel persistently cloudy, emotionally off-kilter, or experience lapses in attention that were never a problem before treatment.

There’s also the cancer itself to consider. Tumours, especially those in the lungs or blood, can release inflammatory molecules into the bloodstream. These molecules travel far beyond the site of the tumour and can affect how neurotransmitters behave, disrupt sleep, and lower the brain’s overall resilience. Even without a single drop of chemotherapy, these factors alone can trigger a noticeable dip in mental clarity.

It’s also important to look at the lived context in which these symptoms occur. The emotional weight of a cancer diagnosis, interrupted sleep patterns, changes in nutrition, and physical fatigue can all compound what’s happening inside the brain.

The result? Patients may begin to doubt their mental abilities, feel anxious about everyday tasks, or withdraw from social or work settings—not because of pain, but because their mind no longer feels familiar.

Yet, for a long time, this phenomenon wasn’t always taken seriously. Complaints about “feeling slow” or “not like myself” were often chalked up to stress or ageing. Thankfully, that’s beginning to change.

Neurocognitive testing is becoming more common in oncology centres, and multidisciplinary teams that include neurologists and psycho-oncologists are helping build clearer frameworks for diagnosing and managing cognitive dysfunction.

Managing these symptoms isn’t about curing them overnight. Even small, well-matched changes can bring meaningful relief. Therapies once used for stroke or brain injuries, like cognitive reha, are now helping cancer survivors regain focus and clarity.

Gentle movement, like walking or yoga, helps improve blood flow to the brain and aids recovery. Simple shifts like using sticky notes, breaking big tasks into steps, or tweaking lighting at home can help patients feel steadier and more capable as they go through the day.

For some, medications that support cognition or mood may be needed for a short period. And increasingly, doctors are looking at ways to time or modify cancer treatment regimens to minimise these side effects when possible, especially in patients who are already vulnerable due to age or pre-existing conditions.

But the first and most important step? Naming it. Giving patients the language to describe what they’re going through. Letting them know it’s not imagined. That their brain function matters just as much as their tumour markers or scan reports.

Because healing from cancer isn’t just about staying alive—it’s about returning to life. And for that, the mind needs to feel sharp, capable, and whole.

Disclaimer: The views expressed in this article are of the author and not of Health Dialogues. The Editorial/Content team of Health Dialogues has not contributed to the writing/editing/packaging of this article.