Cancer treatment side effects: why speaking up early matters

Cancer treatments can cause side effects. Most people know this before treatment even begins. But knowing that side effects can happen is different from knowing what to do when they actually appear.

Whether you are going through treatment yourself or supporting someone you care about, these questions inevitably arise:

Should you call the hospital about the tingling in your fingers? Is tiredness simply something you have to accept? Is skin rash really worth mentioning? And what if telling an oncologist how difficult treatment has become leads them to alter a treatment that is keeping the cancer under control?

These questions often make people keep symptoms to themselves, play them down or wait until their next appointment.

Why side effects go unreported

There are many reasons why someone facing cancer may not share their symptoms with a medical team.

Many patients do not want to worry the people around them or prefer to carry on as normally as possible.

It is also common to think side effects are simply part of cancer treatment and something that must be endured. It can also be difficult to know what truly matters: which symptoms are expected, which are unusual, and which need urgent attention.

Fear also plays a major role. Patients don’t want to put their treatment at risk. If a medicine is successfully controlling the cancer, it is understandable to worry that saying “I am struggling with this” could lead a doctor to lower the dose, interrupt treatment, or stop it altogether.

Previous experiences matter too. If someone has talked about a symptom before but felt that it was not taken seriously, they are less likely to mention it again. They may worry about seeming difficult or taking up too much of their doctor's time.

None of these reactions are unusual. But remaining silent can make it harder for healthcare teams to understand how treatment really affects a person’s daily life and well-being.

How early communication matters

Side effects are not simply an inconvenience alongside cancer treatment. They can affect ordinary daily activities and also directly influence whether a patient feels able to start or continue treatment.

So before starting treatment, it can help to ask:

• Which side effects are common with this treatment?
• Which symptoms should be reported immediately, and which symptoms can wait until the next appointment?
• What can be done if a side effect becomes difficult to manage?

It is important to remember that everyone responds differently. Knowing about possible side effects does not mean someone will experience all of them.

Also, reporting a side effect does not automatically mean stopping treatment. Medical teams have many ways to help patients stay on track:

• prescribe supportive medicines (for instance to manage nausea, pain or skin irritation).
• adjust the dose or schedule.
• temporarily interrupt treatment, or sometimes switch to another treatment, to allow the body to recover.
• involve other medical specialists, such as dermatologists, physiotherapists, dietitians, pain experts and psychologists. The goal is to find the best balance possible: a treatment that is effective , but also one that remains tolerable over time.

Better not wait: why timing matters

Preventing complications before they escalate:

Some side effects require immediate medical attention. Depending on the treatment, these may include fever, signs of infection, unusual bleeding or bruising, severe vomiting, diarrhea, breathing difficulties, or other sudden or severe symptoms.

This said, early reporting also matters for symptoms that are not emergencies. A relatively small problem can sometimes become harder to control if you wait.

Reporting it early gives the care team a chance to investigate it and act before it becomes more troublesome.

Overcoming memory loss

There is another reason not to wait too long: we forget. Research has shown that when people are asked later about symptoms they experienced during chemotherapy, they may remember fewer symptoms or describe them as less severe. Human memory naturally softens past discomfort.

A patient may feel terrible for several days after treatment, but by the time they see their oncologist a few weeks later, they feel better. When asked: “How have you been?”, the answer is often: “Actually, not too bad.”

Keeping a simple symptom diary in a notebook or on a mobile phone can help to keep the picture accurate.

Describing a side effect is not always easy

Doctors frequently ask patients to rate symptoms on a scale from 1 to 10. But what does a fatigue score of 6 mean? One person’s 6 might feel completely different from somebody else's.

It is often easier to describe what has changed in daily life. Ask yourself:

• What can I no longer do that I could do before treatment?
• Is this affecting my work or household activities?
• Am I seeing friends less often?
• Has it stopped me exercising or going outside?
• Is it affecting my sleep, eating or relationships?

Take fatigue as an example.

Saying “I am tired” gives some information.

Saying “I need to sleep for two hours every afternoon” is more detailed.

Saying “I am so exhausted that I have stopped seeing friends and I struggle to cook or work” gives the medical team a clear, actionable picture of how much the treatment is affecting quality of life.

Who can you talk to?

At Anticancer Fund, our core mission is turning evidence into care: we translate scientific evidence into better treatments, improved supportive care, and a higher quality of life for people facing cancer. Open communication about side effects is part of that mission.

Your oncologist should know about important problems, but they do not have to be the only person you speak to. More people can help: Oncology nurses, primary care doctors, pharmacists, physiotherapists or anyone in the medical team.

Patient organisations can help, too. Speaking with people who have similar experiences can help you find words for what you are going through and list questions to discuss with your medical team.

If you or someone close to you needs independent, evidence-based guidance, our My Cancer Navigator service is here to help. We assist patients and their loved ones in understanding what side effects to expect, exploring ways to manage them, and where to find extra support if needed.

Help us turn evidence into care for everyone facing cancer

Knowing how and when to talk about side effects can transform a patient’s treatment journey.

If you find this article helpful, please share it with a friend, family member, or colleague. You might reach someone who is supporting a loved one through cancer treatment right now and needs this advice.

This blog is inspired by a talk given by Dr. Sydney Barned during the 2026 ASCO Annual Meeting.

https://mdnewsline.com/both-sides-of-the-stethoscope-dr-sydney-barned-on-cancer-treatment-toxicity-and-tolerability/ Interview of Dr. Sydney Yolande Barned

https://www.sciencedirect.com/science/article/abs/pii/S146238891000102X Immediate versus delayed self-reporting of symptoms and side effects during chemotherapy: Does timing matter? (2011)

https://pubmed.ncbi.nlm.nih.gov/29725799/ The timeliness of patients reporting the side effects of chemotherapy (2018)