Side effects of targeted therapies

If you are having targeted therapy for breast cancer, you may experience side effects.

Side effects aren't common, but sometimes they can be serious. It is important you ask your doctor or nurse for advice and treatment if you experience anything that is worrying you.

Common side effects

There are several different types of targeted therapies. The side effects for each type and for individual drugs can be different but we list more frequent side effects:

HER2 targeted therapies including trastuzumab (Herceptin), pertuzumab (Perjeta)

CDK4/6 inhibitors 

Antibody drug conjugates (ADCs) including trastuzumab emtansine (Kadcyla), trastuzumab deruxtecan (Enhertu), sacituzumab govitecan (Trodelvy). ADCs are more likely to have specific side effects. Ask your doctor or nurse what to expect. 

Targeted therapy drugs may cause:

• fatigue
• nausea
• aching joints
• fever
• headaches
• dry or itchy eyes
• constipation or diarrhoea
• bleeding and bruising
• high blood pressure.

Side effects of trastuzumab (Herceptin and others)

Trastuzumab is used to treat HER2+ breast cancer. Common brand names for the drug include Herceptin, Herzuma and Ogivri.

Known side effects include:

• reactions related to the infusion - fever, chills, mild aches
• headache
• diarrhoea
• cough
• rash
• heart problems.

There is no increased risk of infection with Herceptin, as it does not usually suppress the immune system.

If you're having trastuzumab with chemotherapy, you may also experience side effects from the chemo. Talk to your treating team as soon as possible about any side effects that are worrying you. Often, it’s possible to manage them effectively, especially if they are addressed early.

Risk of heart problems with trastuzumab

The most significant side effect of trastuzumab is the risk of heart problems, also known as 'cardiotoxicity'.

On average, about 2 to 7% of people will have heart problems from this medication. It’s important to know that these problems usually improve if you take a break from treatment or stop treatment. The risk increases in people who are older, have pre-existing cardiovascular disease, or are already receiving cardiotoxic treatments

If you have a pre-existing heart problem, your doctors may not recommend trastuzumab.

Before you begin treatment, your doctor will check your heart function with an echocardiogram (ECHO) or a multigated acquisition scan (MUGA). They will check it again at regular intervals while you are having treatment.

Monitoring can detect any decline in heart function before you have symptoms. If necessary, your treatment can be changed, stopped, or you may be given medication to protect your heart from further changes. Your doctor may refer you to a cardiologist for further management.

Symptoms of heart problems include:

• shortness of breath
• ankle swelling
• feeling faint 
• tightness in the chest
• chest pains
• an irregular heartbeat.

It’s also important that your blood pressure is controlled, as this can affect how strongly your heart pumps. Your medical oncologist will discuss this with you.

Side effects of trastuzumab emtansine (Kadcyla or TDM1)

Kadcyla is used to treat early and metastatic breast cancer that is HER2+. It can have side effects, but it’s unlikely you will experience all of them.

If the side effects are worrying you or do not go away after a while, you should contact your medical oncologist or speak with a nurse.

Common side effects of T-DM1

You may experience 1 or more of the following:

• tiredness/fatigue
• nausea
• bone and joint pain
• muscle pain
• bruising, nose-bleeds (low blood platelet count)
• headache
• constipation
• tingling and numbness in toes and/or fingers
• breathlessness and looking pale (anaemia)
• abnormal liver function.

TDM1 does not always cause hair loss. If you have lost your hair during chemotherapy, it may grow back.

TDM1 does not usually suppress the immune system, but if you get a temperature over 38 degrees, you should still go to your nearest emergency department.

Rare but serious side effects of T-DM1

About 1% to 2% of people have serious side effects from T-DM1.

Heart problems

Side effects include reduced heart function and congestive heart failure. Watch for signs such as:

• swelling of the ankles or legs
• shortness of breath
• cough
• rapid weight gain.

Reduced heart function often doesn't cause any symptoms. You will have regular heart tests will during treatment to detect any early signs. Your treatment will be adjusted or you will be referred to a cardiologist if necessary.

Lung problems

TDM1 may cause inflammation of the lungs. Symptoms include:

• trouble breathing
• cough
• tiredness
• fluid in the lungs.

Liver problems

Changes in liver function can happen with treatment. Symptoms include:

• swelling or pain in the abdomen
• a yellow tint in the eyes or skin (jaundice)
• swollen legs, feet or ankles.

You will have regular blood tests to monitor for early changes in the liver and other organs.