Talimogene laherparepvec (T-VEC)

Talimogene laherparepvec (T-VEC) is a type of immunotherapy. It is also called Imlygic.

It's a treatment for melanoma skin cancer that has spread to other areas of the skin, soft tissue or the lymph nodes, and can’t be removed with surgery (unresectable).

How does T-VEC work?

T-VEC is a treatment using a weakened form of the cold sore virus. The changed virus grows in the cancer cells and destroys them. It also works by helping the immune system recognise and attack cancer cells.

How do you have T-VEC?

You have T-VEC as an injection directly into the cancer.

Before the injection, you might have a cream to numb the area (local anaesthetic). Sometimes you can have anaesthetic as an injection.

If you need T-VEC into a lymph node, your doctor or surgeon might use an ultrasound scan to help guide the needle if they can’t see or feel the node.

You might have one or several injections depending on the number of areas of melanoma you have. After the injection your doctor presses on the site for about 30 seconds. They clean the area and cover it with an air and water tight dressing.

The dressing stays on for at least 8 days from the last treatment. Or longer if the injection site is weeping or oozing.

How often do you have T-VEC?

After the first injection of T-VEC, you go back 3 weeks later for the second. You then have injections every 2 weeks.

You have T-VEC for at least 6 months. Your doctor may stop T-VEC if it’s no longer helping you or the side effects are too bad.


You might have blood tests before starting treatment and during your treatment. They check your general health and might check your levels of blood cells and other substances in the blood.

What are the side effects of T-VEC?

Side effects can vary from person to person. They also depend on what other treatment you are having. 

This treatment affects the immune system. This may cause inflammation in different parts of the body which can cause serious side effects. They could happen during treatment, or some months after treatment has finished. In some people, these side effects could be life threatening.

When to contact your team

Your doctor, pharmacist or nurse will go through the possible side effects. They will monitor you closely during treatment and check how you are at your appointments. Contact your advice line as soon as possible if:

  • you have severe side effects

  • your side effects aren’t getting any better

  • your side effects are getting worse

Early treatment can help manage side effects better. 

Contact your healthcare team immediately if you have signs of infection, including a temperature above 37.5C or below 36C.

We haven't listed all the side effects here. Remember it is very unlikely that you will have all of these side effects, but you might have some of them at the same time.

Common side effects

These side effects happen in more than 10 in 100 (more than 10%). You might have one or more of them. They include:

Tiredness and weakness

You might feel very tired and as though you lack energy.

Various things can help you to reduce tiredness and cope with it, for example exercise. Some research has shown that taking gentle exercise can give you more energy. It is important to balance exercise with resting.

Flu-like symptoms

About 9 out of 10 (about 90%) of people having T-VEC get flu-like symptoms. Symptoms include a high temperature, headaches, chills, muscle aches, shivering, and feeling tired and weak. These symptoms usually get better after 3 days.

Call your advice line if you have a high temperature or feel unwell.

Feeling or being sick

Feeling or being sick is usually well controlled with anti sickness medicines. It might help to avoid fatty or fried foods, eat small meals and snacks and take regular sips of water. Relaxation techniques might also help.

It is important to take anti sickness medicines as prescribed even if you don’t feel sick. It is easier to prevent sickness rather than treat it once it has started.

Injection site

You might have a reaction to T-VEC at the injection site. This can make the area painful, red, bleed, swell, and may feel warm. It can also cause a discharge or leakage of fluid from the site.

Tell your healthcare team straightaway if there are any problems at the injection site.

Swollen hands and feet

Swelling of hands and feet is due to fluid build up. This is called oedema. Let your doctor or nurse know if you have any swelling.


Tell your healthcare team if you keep getting headaches. They can give you painkillers to help.


Tell your doctor or nurse if you get a cough. It could be a sign of infection. 

Diarrhoea or constipation

Tell your healthcare team if you have diarrhoea or constipation. They can give you medicine to help. 


T-VEC can cause pain in different parts of the body. It's common to feel pain in your muscles, joints, hands, feet, arms or legs with T-VEC.

Less commonly you might have pain from your tumour, ear, tummy (abdomen), back of the throat, back, groin or armpit.

Speak to your doctor or nurse about what painkillers you can take to help with this.

Occasional side effects

These side effects happen in between 1 and 10 out of every 100 people (between 1 and 10%). You might have one or more of them. They include:

  • red, hot, swollen and tender skin caused by infection (cellulitis)
  • cold sores (herpes)
  • infection – this includes infection of the tumour, your upper respiratory tract (throat, sinuses and voice box), and rarely the area where the needle went in
  • a low number of red blood cells (anaemia) – you might feel tired and lack energy
  • a reaction by your immune system causing inflammation, such as, inflammation of your lungs or kidneys, your blood vessels becoming narrow or block (vasculitis) or worsening of skin conditions (psoriasis and vitiligo)
  • lack of fluid in your body (dehydration) – you might feel thirsty, dizzy, confused, have a very dry mouth, your urine might be dark or you may not be going very much
  • feeling confused, anxious or low in mood (depression)
  • dizziness - don’t drive or operate heavy machinery if you have these problems
  • difficulty in sleeping (insomnia)
  • fast heart rate
  • high blood pressure - symptoms include headaches, nosebleeds, blurred or double vision or shortness of breath
  • flushing of the skin
  • shortness of breath
  • skin problems – your skin might have patchy white areas (vitiligo), or a rash that could be itchy, red, sore, swollen and blister. Rarely you might develop a rash in the shape of a circle with small bumps
  • generally feeling unwell
  • losing weight
  • wound problems such as bruising, pain, ooze or discharge
  • blood clots that are life threatening: signs are pain, swelling and redness where the clot is. Feeling breathless can be a sign of a blood clot on the lung. Contact your advice line or doctor straight away if you have any of these symptoms

Rare side effects

These side effects happen in fewer than 1 in 100 people (fewer than 1%). You might have one or more of them. They include:

  • cancerous white blood cells near or at the injection site (plasmacytoma)
  • an allergic reaction - you may get a rash, shortness of breath, redness or swelling of the face
  • herpes eye infection (keratitis herpes)
  • difficulty breathing due to narrowing or blocked airways

Coping with side effects

We have more information about side effects and tips on how to cope with them.

What else do you need to know?

Other medicines, foods and drink

Cancer drugs can interact with medicines, herbal products, and some food and drinks. We are unable to list all the possible interactions that may happen. An example is grapefruit or grapefruit juice which can increase the side effects of certain drugs.

Tell your healthcare team about any medicines you are taking. This includes vitamins, herbal supplements and over the counter remedies. Also let them know about any other medical conditions or allergies you may have.

Preventing close contacts getting an infection

To help prevent a close contact getting an infection from T-VEC there are things you can do to help lower the risk. While having this treatment and for 30 days after the last injection you should avoid:

  • sexual intercourse without a condom
  • kissing if either person has broken skin
  • using the same cutlery, crockery, cups and glasses
  • other people touching the injected site

Loss of fertility

It is not known whether this treatment affects fertility in people. Talk to your doctor before starting treatment if you think you may want to have a baby in the future.

Pregnancy and contraception

It is unknown whether treatment may or may not harm a baby developing in the womb. It is important not to become pregnant or father a child while you are having treatment.

Talk to your doctor or nurse about effective contraception you can use during treatment. Ask how long you should use it before starting treatment and after treatment has finished. Let them know straight away if you or your partner falls pregnant while having treatment.

Doctors recommend that you use a condom while on treatment in case the drug can be passed on during sexual contact. 


It is not known whether this drug comes through into the breast milk. Doctors usually advise that you don’t breastfeed during this treatment.

Treatment for other conditions

If you are having tests or treatment for anything else, always mention your cancer treatment. For example, if you are visiting your dentist.


Don’t have immunisations with live vaccines while you’re having treatment and for up to 12 months afterwards. The length of time depends on the treatment you are having. Ask your doctor or pharmacist how long you should avoid live vaccinations.

In the UK, live vaccines include rubella, mumps, measles, BCG, yellow fever and one of the shingles vaccines called Zostavax.

You can have:

  • other vaccines, but they might not give you as much protection as usual
  • the flu vaccine (as an injection)
  • the coronavirus (COVID-19) vaccine - talk to your doctor or pharmacist about the best time to have it in relation to your cancer treatment

Members of your household who are aged 5 years or over are also able to have the COVID-19 vaccine. This is to help lower your risk of getting COVID-19 while having cancer treatment and until your immune system Open a glossary item recovers from treatment.

Contact with others who have had immunisations - You can be in contact with other people who have had live vaccines as injections. Avoid close contact with people who have recently had live vaccines taken by mouth (oral vaccines) such as the oral typhoid vaccine. Sometimes people who have had the live shingles vaccine can get a shingles type rash. If this happens they should keep the area covered.

If your immune system is severely weakened, you should avoid contact with children who have had the flu vaccine as a nasal spray as this is a live vaccine. This is for 2 weeks following their vaccination.

Babies have the live rotavirus vaccine. The virus is in the baby’s poo for about 2 weeks and could make you ill if your immunity is low. Get someone else to change their nappies during this time if you can. If this isn't possible, wash your hands well after changing their nappy.

More information about this treatment

For further information about this treatment and possible side effects go to the electronic Medicines Compendium (eMC) website. You can find the patient information leaflet on this website.

You can report any side effect you have to the Medicines Health and Regulatory Authority (MHRA) as part of their Yellow Card Scheme.

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