FDA Approval: Talimogene laherparepvec (Imlygic) for Melanoma

A virus, licensed as a drug

On October 27, 2015, the FDA approved talimogene laherparepvec, sold as Imlygic and often shortened to T-VEC. NCI reported it as the first oncolytic virus therapy cleared in the United States. An oncolytic virus is a virus altered in the lab so that it grows inside tumor cells and bursts them.

The approved use is narrow, and the label spells it out. Imlygic is for the local treatment of melanoma lesions in the skin, just under the skin, and in lymph nodes, in people whose melanoma has come back after their first surgery and cannot be cut out.

What it is made from

The label describes Imlygic as a live, weakened herpes simplex virus type 1 — the cold-sore virus — that has been genetically changed in two ways. Some genes were deleted so it grows in tumors rather than in normal tissue. A human gene was added so the virus makes GM-CSF, a protein that calls immune cells in.

The idea is that the virus splits tumor cells open, spilling out fragments the immune system can learn to recognize, while the GM-CSF draws immune cells to the scene. The label is candid that the exact mechanism is unknown. Our page on immunotherapy explains the wider family of treatments that work this way.

The trial the approval rests on

The FDA relied on one open-label randomized study. It enrolled 436 people with stage IIIB, IIIC, or IV melanoma that surgeons could not remove. Two hundred and ninety-five got Imlygic injected into skin, subcutaneous, or lymph node lesions. The other 141 got GM-CSF as a shot under the skin.

The main measure was durable response rate: the share of people whose tumors shrank by enough to count as a complete or partial response and stayed that way for at least six months. It was 16.3% with Imlygic and 2.1% with GM-CSF. Median time to a response was 4.1 months.

Overall survival did not differ. Median survival was 22.9 months with Imlygic and 19.0 months with GM-CSF, a gap the trial could not call real.

People with active brain metastases, bone metastases, extensive disease in the internal organs, eye or mucosal melanoma, or a suppressed immune system were kept out of the trial.

What treatment involves

Imlygic is injected directly into the lesion. The label says it must never go into a vein.

The first injection uses a weak preparation. Three weeks later the strength goes up sharply, and injections then continue every two weeks. There is a ceiling on the total volume that can go in at one visit, so not every lesion can be treated every time. In the trial the median time on treatment was 23 weeks.

The product is shipped and stored frozen at minus 90 to minus 70 degrees Celsius, and thawed just before use.

Who cannot have it, and who has to be careful

Because it is a live virus, the contraindications are firm. The label says do not give Imlygic to people who are immunocompromised, including those with leukemia, lymphoma, HIV, or on immune-suppressing drugs, because it may cause life-threatening spreading herpes infection. It must not be given during pregnancy.

The label also warns about accidental exposure. Health workers and close contacts should avoid touching injected lesions, dressings, or body fluids. Staff who are pregnant or immunocompromised should not prepare or give it.

The most common side effects, each in at least a quarter of people, were fatigue, chills, fever, nausea, flu-like illness, and pain at the injection site. Most were mild or moderate and settled within 72 hours. The most common serious one was cellulitis, a spreading skin infection.

The wider picture

The 112,000 new US melanoma diagnoses and 8,510 deaths expected in 2026 are American Cancer Society estimates, which SEER republishes. Five-year relative survival across all stages, for cases diagnosed in 2016 through 2022, is 94.7%.

Stage drives that. Localized melanoma sits at 100.0%, regional at 76.0%, distant at 34.0%. About 77% of cases are found while still localized. Imlygic is aimed at the much smaller group whose disease has spread through skin and nodes but cannot be removed. Our page on melanoma stages sets out the full system.

These are group figures from past years. They do not describe any one person, and they predate several newer melanoma drugs.

What this does and doesn't change

The label carries an unusual limitation of use, printed in the indication itself: Imlygic has not been shown to improve overall survival, and has no effect on metastases in the internal organs. That is the drug's own manufacturer's language, agreed with the FDA.

So the honest summary is that this treatment shrinks injectable lesions in a minority of people and keeps them shrunk, which can matter a great deal when those lesions are painful, bleeding, or disfiguring. It is not a systemic melanoma treatment, and it does not replace one.

• Approval sets out who is eligible in general terms. Whether it fits one person is a clinical judgment made with an oncologist.
• The trial compared Imlygic with GM-CSF, not with modern checkpoint inhibitors.
• Labels change. The version cited here is the one on DailyMed at the source-check date.

When to get checked

Melanoma is found by looking. Ask a clinician about any mole or spot with:

• Asymmetry, so one half does not match the other
• An irregular, ragged, or blurred border
• More than one color, or an uneven color
• A diameter over about 6 mm, roughly a pencil eraser
• Any change in size, shape, color, or feel, or new itching, bleeding, or crusting

NCI packs these into the letters ABCDE, and adds two more signs: a mole that itches, oozes, bleeds, or opens up, and new moles growing next to an existing one. A spot that looks unlike every other spot on your body is worth showing to a doctor even if it breaks none of these rules. Our page on changes in a mole or skin has more.

Sources

• NCI Cancer Currents, FDA Approves Talimogene Laherparepvec to Treat Metastatic Melanoma — https://www.cancer.gov/news-events/cancer-currents-blog/2015/t-vec-melanoma
• DailyMed, IMLYGIC (talimogene laherparepvec) prescribing information — https://dailymed.nlm.nih.gov/dailymed/services/v2/spls/64ffb680-ea8c-42fc-9649-9e8c0eb77ddb.xml
• NCI PDQ, Melanoma Treatment (Patient Version) — https://www.cancer.gov/types/skin/patient/melanoma-treatment-pdq
• SEER Cancer Stat Facts, Melanoma of the Skin — https://seer.cancer.gov/statfacts/html/melan.html

How this article was prepared

An AI-assisted editorial system helped prepare this page. No named medical reviewer has reviewed it unless one is listed.

The National Cancer Information Foundation publishes Cancer Explained. This page is for learning. It is not medical advice and does not suggest a test or treatment.

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