The short answer
Imlygic (Talimogene laherparepvec) is a type of immunotherapy made from a modified virus. It is a weakened, lab-modified cold-sore virus injected into melanoma tumors, where it multiplies inside cancer cells, bursts them, and signals the immune system to attack. It is a local treatment for melanoma lesions in the skin, under the skin and in lymph nodes that surgery cannot remove, in melanoma that has come back after an earlier operation. The label states it has not been shown to improve overall survival or to affect melanoma in internal organs. Like all cancer medicines it can cause side effects; this page explains the common ones and the warning signs to report. It is educational only and not a substitute for your care team's advice.
Imlygic is the brand name; its generic name is talimogene laherparepvec.
It is a type of immunotherapy made from a modified virus — it is a weakened, lab-modified cold-sore virus injected into melanoma tumors, where it multiplies inside cancer cells, bursts them, and signals the immune system to attack.
It treats melanoma lesions in the skin, under the skin and in lymph nodes that surgery cannot remove, after melanoma has come back following an earlier operation.
It is usually given as an injection directly into melanoma tumors.
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The full explanation.
A cold-sore virus rebuilt to attack melanoma
Talimogene laherparepvec is a living, weakened herpes simplex type 1 virus — the virus behind cold sores — changed in a laboratory.
Some of its own genes were taken out, so it struggles to grow in healthy cells but still multiplies inside cancer cells. A human gene was added in their place. That gene makes GM-CSF, a signal that calls immune cells in.
So the virus fills a melanoma cell and bursts it. The debris, plus the GM-CSF, gives the immune system something to recognize. Imlygic is the brand name.
What the label says it has not been shown to do
This is the sentence most summaries leave out, and it changes how you should read everything else.
The FDA label carries a limitation of use: talimogene laherparepvec has not been shown to improve overall survival, and it has not been shown to affect melanoma that has spread to internal organs.
The approved job is local. It treats melanoma lesions in and just under the skin, and in lymph nodes, that surgery cannot remove and that have come back after an earlier operation. It is not a whole-body treatment, and it is not a substitute for one.
Who cannot have it
Because it is a live virus, two groups are ruled out entirely.
People whose immune system is suppressed cannot have it. That includes people with an inherited or acquired immune deficiency, leukemia, lymphoma, HIV, or anyone taking medicines that damp the immune system down. In them, the virus can spread through the body, and that has been fatal.
People who are pregnant cannot have it either.
Tell your team about steroids, transplant medicines and any immune-suppressing drug you take, even a short course.
Injections into lesions you can see or feel
There is no drip and no tablet. A clinician injects the liquid straight into melanoma lesions in the skin or lymph nodes, using a fine needle and sometimes ultrasound for deeper ones.
The first visit uses a lower strength. Three weeks later comes a stronger dose, and after that visits are roughly every two weeks. The number of lesions injected and the volume depend on their size.
The product is stored in a deep freezer, at around minus 90 to minus 70 degrees Celsius, and thawed just before use. That is why appointments are not easy to move at short notice.
Keeping the virus away from other people
This part is unusual, and it is worth taking seriously. The virus can pass to other people through contact with an injection site or its dressings.
- Keep the treated areas covered with an airtight, watertight dressing for at least the first week after each visit, or longer if the site is weeping.
- If a dressing comes loose, replace it. Wear gloves, then wash your hands.
- Do not touch or scratch the injection sites.
- Put used dressings and gloves in a sealed bag before binning them.
- Keep close contacts who are pregnant, newborn, or immune-suppressed away from the sites and dressings.
Staff who are pregnant or immune-suppressed do not prepare or give this treatment for the same reason.
If you or a close contact develops a cold sore, an ulcer, or an eye infection, contact your team. It may be an ordinary herpes infection. The label notes that this virus is sensitive to acyclovir, so antiviral treatment can also blunt how well the therapy works. That trade-off is your team's call, not one to make at a pharmacy counter.
Flu-like days after each visit
Tiredness, chills, fever, aching and nausea are the usual effects, and they cluster in the day or two after treatment. Injection sites can be sore.
Two less common problems belong in the label. Sores at an injection site can become infected or heal slowly, and that has to be weighed before carrying on. And lesions near a major airway need care, because airway blockage has been reported.
When to get help sooner
- Call 911 or go to an emergency department if your breathing becomes noisy or blocked, especially when a treated lesion sits near your windpipe or throat.
- Call 911 or go to an emergency department if a fever comes with shaking chills and you feel suddenly and badly unwell, or you are dizzy, confused, or breathing fast. Those together can mean an infection spreading into the blood, which will not wait for a clinic slot.
- Call your care team the same day if an injection site turns hot, spreads red beyond its edge, weeps pus, or your temperature reaches 100.4°F (38°C) or higher. Ring the same day as well for a painful red eye or light hurting your eyes, in you or in a close contact.
- Call your care team within a day or two if a treated site will not close over, a dressing keeps lifting off a weeping lesion, or someone in your household develops a cold sore or an unexplained ulcer.
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Common questions
What is Imlygic?
Imlygic (Talimogene laherparepvec) is a type of immunotherapy made from a modified virus. It is a weakened, lab-modified cold-sore virus injected into melanoma tumors, where it multiplies inside cancer cells, bursts them, and signals the immune system to attack. It treats melanoma lesions in the skin, under the skin and in lymph nodes that surgery cannot remove, after melanoma has come back following an earlier operation.
How is Imlygic given?
It is usually given as an injection directly into melanoma tumors. A clinician injects it into tumors you can see or feel in the skin or lymph nodes, repeated on a schedule. It is a local treatment given in the clinic. The exact schedule is set by your care team.
What are the common side effects of Imlygic?
Commonly reported side effects include tiredness, chills, fever, flu-like feelings, and injection-site pain. Not everyone gets them, and many can be managed. Tell your care team about anything new or worsening.
Does Imlygic cure cancer?
That depends on the person, the cancer type, and its stage. For some people a medicine like this can control cancer for a long time or be part of a curative plan; for others the goal is to slow the cancer or ease symptoms. Your care team can explain the goal in your situation.
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Sources last checked: 2026-07-14 what this meansLast updated: 2026-08-13Next planned review: 2027-01-14
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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