Trastuzumab emtansine side effects: the complete list and timeline

Trastuzumab emtansine, also called T-DM1 or Kadcyla, joins a HER2 antibody to a chemotherapy medicine called DM1. Because the chemotherapy is mostly delivered to HER2-positive cancer cells, many people find it gentler than the chemotherapy they had before. It still has side effects, though, and knowing them helps you plan. The most common are tiredness, feeling sick, headache, constipation, muscle and joint aches, nosebleeds, and changes on blood tests, especially low platelets and raised liver enzymes. Some people get tingling or numbness in the hands and feet, dry mouth, mouth sores, taste changes, trouble sleeping or dry eyes. Significant hair loss is uncommon. Less common but important effects include reactions during the drip, a fall in heart pumping strength, inflammation of the lungs, serious bleeding and serious liver problems. T-DM1 can harm an unborn baby, so reliable contraception is needed during treatment and for seven months afterwards. Side effects tend to follow a pattern within each three-week cycle: tiredness and nausea in the first few days, a dip in platelets and a rise in liver tests around the first week, and recovery before the next dose. Some effects, such as nerve changes and tiredness, can build up over several cycles. Your team checks blood tests before each dose and repeats heart scans every few months, so many problems are found before you notice them.

Many find it gentler than earlier chemotherapy

Heavy hair loss and severe sickness are less common, but tiredness is frequent.

Blood tests matter

Low platelets and liver changes often cause no symptoms, so regular tests pick them up.

Some effects build over time

Nerve changes and tiredness may increase across cycles, so keep your team updated.

A list tells you what has been seen across many people. It cannot tell you exactly what you will experience.

Everyone is different

Some people have very few side effects. Others find tiredness or nerve changes hard going. Earlier treatment, age and general health all play a part.

Gentler is not the same as easy

T-DM1 is often easier than earlier chemotherapy, but it is still a chemotherapy-based treatment, and it is fine to find it tiring.

Rare effects do happen

Serious liver, lung, heart or bleeding problems are uncommon, but they are the reason for regular tests and quick reporting.

What this page cannot tell you

It cannot tell you which effects you will get or how severe they will be. Your team can explain your own risks.

Many side effects respond well to simple steps and supportive medicines. Ask your team rather than putting up with them.

Tiredness

Short daily walks, regular sleep times and planning rest around busy days often help more than complete rest.

Nausea and constipation

Small frequent meals, plenty of fluids and fibre, and anti-sickness or bowel medicines from your team can make the first days of each cycle easier.

Mouth and eyes

Rinse your mouth often, use a soft toothbrush, and ask about lubricating eye drops if your eyes feel dry or gritty.