• Keep this leaflet. You may need to read it again.
• If you have any further questions, ask your doctor or nurse.
• If you get any side effects, talk to your doctor or nurse. This includes any possible side effects not listed in this leaflet. See section 4.

1. What Enhertu is and what it is used for
2. What you need to know before you are given Enhertu
3. How you are given Enhertu
4. Possible side effects
5. How to store Enhertu
6. Contents of the pack and other information

Enhertu is a cancer medicine that contains the active substance trastuzumab deruxtecan. One part of the medicine is a monoclonal antibody that attaches specifically to cells that have the protein HER2 on their surface (HER2-positive), as some cancer cells do. The other active part of Enhertu is DXd, a substance that can kill cancer cells. Once the medicine has attached to HER2-positive cancer cells, the DXd enters the cells and kills them.

Enhertu is used to treat adults who have:

• HER2-positive breast cancer that has spread to other parts of the body (metastatic disease) or cannot be removed by surgery, and tried one or more other treatments specifically for HER2-positive breast cancer.
• HER2-low breast cancer that has spread to other parts of the body (metastatic disease) or cannot be removed by surgery and received prior therapy for metastatic disease, or your disease has returned during or within 6 months of completing adjuvant chemotherapy (after surgery). A test will be performed to make sure Enhertu is right for you.
• HER2-mutant non-small cell lung cancer that has spread to other parts of the body or cannot be removed by surgery and who have tried a prior treatment. A test will be performed to make sure Enhertu is right for you.
• HER2-positive stomach cancer that has spread to other parts of the body or to areas near the stomach that cannot be removed by surgery and who have also tried another treatment specifically for HER2-positive stomach cancer.

• if you are allergic to trastuzumab deruxtecan or any of the other ingredients of this medicine (listed in section 6).

If you are not sure if you are allergic, talk to your doctor or nurse before you are given Enhertu.

Talk to your doctor or nurse before you are given Enhertu, or during treatment, if you have:

• cough, shortness of breath, fever, or other new or worsening breathing problems. These may be symptoms of a serious and potentially fatal lung disease called interstitial lung disease. A history of lung disease or kidney problems may increase the risk of developing interstitial lung disease. Your doctor may have to monitor your lungs while you are taking this medicine.
• chills, fever, sores in your mouth, stomach pain or pain when urinating. These may be symptoms of an infection caused by a reduced number of white blood cells called neutrophils.
• new or worsening shortness of breath, cough, tiredness, swelling of ankles or legs, irregular heartbeat, sudden weight gain, dizziness, or loss of consciousness. These may be symptoms of a condition in which your heart cannot pump blood well enough (decreased left ventricular ejection fraction).
• liver problems. Your doctor may have to monitor your liver while you are taking this medicine.

Your doctor will carry out tests before and during treatment with Enhertu.

Enhertu is not recommended for anyone under the age of 18 years. This is because there is no information on how well it works in this age group.

Tell your doctor or nurse if you are taking, have recently taken or might take any other medicines.

• Pregnancy
  Enhertu is not recommended during pregnancy because this medicine may harm the unborn baby.
  Speak with your doctor immediately if you are pregnant, think you may be pregnant or are planning to become pregnant before or during treatment.
• Breast-feeding
  You should not breast-feed during treatment with Enhertu and for at least 7 months after your last dose. This is because it is not known whether Enhertu passes into breast milk. Talk to your doctor about this.
• Contraception
  Use effective contraception (birth control) to avoid becoming pregnant while being treated with Enhertu.
  Women taking Enhertu should continue contraception for at least 7 months after the last dose of Enhertu.
  Men taking Enhertu whose partner may become pregnant should use effective contraception:
  
  • during treatment and
  • for at least 4 months after the last dose of Enhertu.
  
  Talk to your doctor about the best contraception for you. Also talk to your doctor before you stop your contraception.
• Fertility
  If you are a man being treated with Enhertu, you should not father a child for 4 months after treatment and take advice on conserving sperm before treatment because the medicine may reduce your fertility. Therefore, discuss this with your doctor before starting treatment.

Enhertu is not likely to reduce your ability to drive or use machines. Be careful if you feel tired, dizzy, or have a headache.

Contact your doctor right away to reschedule your appointment.

It is very important that you do not miss a dose of this medicine.

Do not stop treatment with Enhertu without checking with your doctor.

The frequency and severity of side effects may vary with the dose you received. Tell your doctor or nurse if you notice any of the following side effects:

Very common (may affect more than 1 in 10 people)

• nausea (feeling sick), vomiting
• tiredness
• decreased appetite
• blood tests showing decreased red or white blood cells, or platelets
• hair loss
• diarrhoea
• constipation
• blood tests showing increased levels of the liver enzymes such as transaminases
• pain in muscles and bones
• weight loss
• fever
• abdominal (belly) pain
• infections of the nose and throat, including flu-like symptoms
• headache
• blisters in or around your mouth
• cough
• blood tests showing low blood potassium levels
• indigestion
• infection of the lungs
• breathing difficulties
• nosebleed
• swelling of ankles and feet
• dizziness
• altered/bad taste in mouth

Common (may affect up to 1 in 10 people)

• rash
• blood tests showing increased levels of bilirubin, alkaline phosphatase or creatinine
• itching
• dry eye
• skin discolouration
• blurred vision
• feeling thirsty, dry mouth
• bloating
• fever along with a decreased number of white blood cells called neutrophils
• inflammation of the stomach
• excessive gas in the stomach or intestine
• reactions related to the infusion of the medicine which may include fever, chills, flushing, itching or rash

If you get any side effects, talk to your doctor or pharmacist. This includes any possible side effects not listed in this leaflet. You can also report side effects directly via the Yellow Card Scheme Website: www.mhra.gov.uk/yellowcard or search for MHRA Yellow Card in the Google Play or Apple App Store. By reporting side effects you can help provide more information on the safety of this medicine.

• The active substance is trastuzumab deruxtecan.
  One vial of powder for concentrate for solution for infusion contains 100 mg of trastuzumab deruxtecan. After reconstitution, one vial of 5 mL solution contains 20 mg/mL of trastuzumab deruxtecan.
• The other ingredients are L-histidine, L-histidine hydrochloride monohydrate, sucrose, polysorbate 80.

Enhertu is a white to yellowish-white lyophilised powder supplied in a clear amber vial with a rubber stopper, aluminium seal and plastic flip-off cap.

Each carton contains 1 vial.