When someone says the word “cancer,” particularly “breast cancer,” your reality is instantly filled with medical jargon, treatment plan options, and choices you never imagined having to make. One of the names you will learn early on, particularly if your breast cancer is HER2-positive, is Trastuzumab.

Let’s take a step-by-step on what it is, how it works, why it’s so vital, and what to expect if Trastuzumab enters your treatment plan.

So, what is Trastuzumab?
Trastuzumab (tras-TOO-zoo-mab) is a type of targeted therapy. It’s also known by the brand name Herceptin.

It’s not chemo, but it’s usually used with chemo to treat a certain kind of breast cancer, referred to as HER2-positive breast cancer. This is a type of cancer with elevated levels of a protein named HER2 (short for Human Epidermal Growth Factor Receptor 2), which promotes cancer cells to grow more quickly.

Trastuzumab’s role is to bind to and block the HER2 protein so the cancer cells cannot grow and divide as aggressively.

That is, it’s like locking a door that cancer prefers to continue walking through.

Who Needs Trastuzumab?
Trastuzumab is administered to patients diagnosed with HER2-positive breast cancer. Approximately 1 out of 5 breast cancers are HER2-positive, and this kind will develop and spread faster than HER2-negative cancers.

Doctors will check your tumour tissue following biopsy or surgery to determine if it’s HER2-positive. If so, this could be suggested as part of your treatment plan, either:
Before surgery (neoadjuvant therapy) to reduce the tumour.
Following surgery (adjuvant therapy) to reduce the chance of recurrence
Or with advanced or metastatic breast cancer to control the condition and prolong life

How Does It Work
Imagine cancer cells to be naughty kids. HER2-positive cancer cells are the children who have had far too much sugar, they grow rapidly, won’t listen, and won’t stop.

Trastuzumab binds to the HER2 protein perched on the surface of the cancer cells. This prevents the cancer cells from getting the signals to multiply. But that’s not all, it also marks the cancer cells so your immune system can move in and kill them.

So it’s sort of doing double duty: growth blocking and assisting your body in fighting back.

How Is It Given?
Trastuzumab is administered by intravenous (IV) infusion, typically in a hospital or infusion clinic. The initial dose takes longer, approximately 90 minutes, since your healthcare team will be keeping a close watch on you for side effects. Subsequent doses can then take 30 to 60 minutes.

It’s typically administered:
Every three weeks
Or once weekly, depending on your regimen
Most patients get Trastuzumab for a year after surgery, even if the cancer is no longer present because it decreases the risk of the cancer returning.

Some of the newer versions, such as Phesgo, put Trastuzumab together with another medication (pertuzumab) in a subcutaneous (skin) injection. This new form can take only 5–8 minutes, which is a great relief for a lot of patients.

Does It Have Side Effects?
Yes, but they are generally less severe than the side effects of chemotherapy. Everyone gets along pretty well on Trastuzumab. But here are a few things to be aware of:
Common side effects are:
Chills or fever after the initial dose
Fatigue
Diarrhea
Headache
Nausea
More severe but less common side effects:
Heart issues, particularly in individuals who’ve had some types of chemotherapy (such as anthracyclines)
Allergic reactions during or after the infusion (closely watched by nurses)
Breathing difficulties (extremely rare, but serious)
Your healthcare team will most probably check your trastuzumab heart function (with procedures such as an echocardiogram) before and during treatment. If things are not normal on any test, they may stop or change your treatment.

Living with Trastuzumab: What to Expect
One of the most significant facts to learn is that Trastuzumab is not chemo, although it’s sometimes administered during chemotherapy. It doesn’t result in hair loss, and a lot of patients can work, take care of families, and maintain daily life while on it.

But, hey, it’s only natural to feel emotionally and physically drained at this stage of treatment. You’ve already had surgery, chemo, or radiation, so another year of infusions can feel daunting.

That’s fine. Be kind to yourself.
Patients have used the term “maintenance mode” to describe this stage. You’re not battling the detectable tumour anymore, but you’re strengthening the fortifications and constructing your defence mechanisms.

It’s just as critical, and you’re still in healing mode.

The Good News: It Works
Before Trastuzumab, HER2-positive breast cancer was worse off than others. But since its use was approved early in the 2000s, Trastuzumab has changed the face of survival rates and recurrence.

It’s one of the biggest success stories in contemporary cancer care, and it keeps saving lives every day.

If you’re on Trastuzumab, you’re taking a targeted, intelligent therapy that’s made HER2-positive breast cancer a whole lot more treatable.

Can I Still Have a Normal Life on Trastuzumab?
Absolutely. You might need to schedule around infusion days, rest more, and be mindful of your heart health, but many people live full, active lives in the middle of and after treatment.
Here are a few tips:
Stay on top of all your follow-up appointments and heart checkups.
Let your team know if you feel extra tired or short of breath.
Stay hydrated and eat balanced meals.
Be gentle with yourself—healing is not linear.
Ask about any support services or mental health resources available.

Final Thoughts
Hearing that you need Trastuzumab can be overwhelming, but it’s also a sign that there’s a powerful tool available to help treat your specific cancer.

You are not alone. Your care team, your support network, and even your own body are all working together to see you through this phase. Trastuzumab is one additional teammate on your side, simply doing its work.