Not Just Chemo: The Overlooked Side Effects of Immunotherapy and Targeted Treatment

When people talk about cancer side effects, they’re usually talking about chemotherapy. Hair loss. Nausea. Fatigue. The full horror show. But if you’re having immunotherapy or a targeted therapy like bevacizumab, the side effects are a different beast entirely and they don’t always get the attention they deserve.

Sometimes, you’re doing both chemo and immunotherapy or targeted treatments at the same time, which makes it even harder to tell what’s causing what. You just know your body is flipping out, and your oncologist is looking at you like, “Hmm, that’s rare.” Cool. Comforting.

So what exactly is immunotherapy and targeted therapy?

Immunotherapy is designed to help your immune system recognise and attack cancer cells. Think of it like giving your immune system night-vision goggles and saying, “That’s the enemy, go get it.” The most common immunotherapy drugs used in bowel cancer are checkpoint inhibitors like nivolumab and pembrolizumab, usually reserved for people with a high MSI or dMMR tumour.

Targeted therapies, like bevacizumab (Avastin) or cetuximab, don’t mess with your immune system. They target specific proteins or pathways that help cancer grow. These drugs are often used in combination with chemo, especially in stage 4 bowel cancer.

The short version? They’re not chemo. But they still come with side effects. And some of those side effects can be weird, unexpected, or delayed.

Common immunotherapy side effects

The irony of immunotherapy is that you’re not just turning your immune system on, sometimes you’re turning it against yourself. These drugs can cause your immune system to attack healthy cells, leading to what’s called immune-related adverse events (irAEs).

Common issues include:

• Skin rashes or itching – sometimes mild, sometimes full-body nightmares
• Diarrhoea or colitis – inflammation of the bowel, not ideal when you already have bowel cancer
• Fatigue – different from chemo fatigue, often described as flu-like
• Endocrine problems – like thyroid issues or adrenal insufficiency, which can mess with your whole body
• Liver inflammation – usually picked up in blood tests before you feel it
• Lung inflammation (pneumonitis) – rare but serious

The scary part? Some of these side effects can show up weeks or even months after your treatment starts, or even after it ends.

Common targeted therapy side effects

Targeted therapies have their own mixed bag of reactions. Since they don’t destroy healthy cells like chemo does, the side effects tend to be more specific and sometimes less severe, but that doesn’t mean they’re easy.

Here’s what people on drugs like bevacizumab or cetuximab often deal with:

• Skin issues – dry, cracking skin or an acne-like rash, especially on the face and chest
• High blood pressure – common with bevacizumab
• Mouth sores
• Slow wound healing or bleeding problems – especially if you’re having surgery
• Hand-foot syndrome – red, sore, peeling skin on your palms and soles

Bevacizumab can also increase the risk of clots or bowel perforation (a rare but serious side effect where your bowel wall tears). Sounds like a horror story, but it’s important to know so you can spot the signs early.

“I thought that was from the chemo…”

Let’s be real, if you’re on multiple treatments, side effects blur together. It’s easy to assume the exhaustion, the rash, or the gut flare-up is from chemo, because that’s the one everyone warns you about.

But if you’re still getting side effects after chemo has finished, or they’re showing up out of nowhere, it could be the immunotherapy or targeted drugs. Some patients find that once chemo is paused, the immunotherapy side effects suddenly become more obvious. Others have symptoms pop up months into treatment, which makes it even harder to connect the dots.

How to track what’s what

If you’re on a combination of treatments, start a simple symptom tracker. It doesn’t need to be fancy, just jot down:

• What symptoms you notice
• When they started
• What day of your treatment cycle it is
• Whether they’re getting better or worse

This info can help your oncologist figure out whether it’s chemo, immunotherapy, or something else. And if it turns out to be immune-related, catching it early can be the difference between managing it with tablets or needing to stop treatment entirely.

When to call your doctor

If in doubt, speak up. Here are some red flags that need a call (or even a trip to the hospital):

• Sudden, severe diarrhoea or ongoing stomach pain
• Shortness of breath or chest pain
• Yellowing of the skin or eyes (jaundice)
• Unusual fatigue or dizziness that feels worse than normal
• Persistent rash, especially if painful or spreading

And don’t wait days to see if it goes away. If it’s immune-related, earlier intervention usually means better outcomes and fewer long-term problems.

Emotional impact: It’s not “just a rash”

One of the hardest things is feeling like your side effects don’t count unless they’re dramatic. Hair falling out? People understand. But constant gut inflammation or a painful skin reaction? That gets less sympathy, or worse, it gets brushed off as “just part of the process.”

But these side effects can seriously mess with your quality of life. Some can even be permanent. So it’s okay to be frustrated. It’s okay to be over it. And it’s okay to ask for more help than you think you’re “allowed” to need.

Final thought

If you’re going through immunotherapy or targeted therapy, you’re not making it up. Side effects are real, even if they don’t get the same airtime as chemo. They can be sneaky, subtle, or sudden and they matter.

Keep speaking up. Keep tracking what’s happening. And remember, you’re not weak for struggling. These aren’t easy treatments. But knowing what to watch for can give you just a little more control in a world that often feels like it’s spinning.

Need to talk it through? Bowel Cancer Australia’s nurse and support team can be reached on 1800 555 494, they’re legends.