Oncolytic virus therapy

This page was reviewed under our medical and editorial policy by

David Winchester, MD, FACS, C0-Medical Director, Breast Program | Chicago

Evan Pisick, MD, Chief of Medical Oncology, City of Hope | Chicago

This page was updated on September 12, 2023.

Certain viruses are known to infect and kill tumor cells. Researchers have been able to modify some of these viruses found in nature and inject them into cancer cells, causing the cancer cells to die.

A group of viruses known as oncolytic viruses (OVs) are being used to treat cancer, particularly advanced metastatic melanoma.

The first oncolytic virus therapy approved by the U.S. Food and Drug Administration for the treatment of melanoma is Imlygic® (talimogene laherparepvec, or T-VEC).

Other OVs are in various stages of development.

A type of immunotherapy, OVs are considered for melanoma patients who have:

  • Tumors that can’t be removed by surgery
  • Tumors that recur

Imlygic® is based on a herpes simplex virus type 1. Its gene code has been modified to stimulate the production of immune cells.

When a tumor cell is infected by the virus, it makes multiple copies of itself. The large number of copies causes the cell to burst and die. When the tumor cell dies, it releases materials (such as tumor antigens) that the immune system recognizes, and the immune system is called into action. The immune response may be local (killing nearby tumor cells) or systemic (killing cancer cells elsewhere in the body).

Oncolytic virus therapy isn’t new. Doctors have long seen that viruses may cause cancer patients to go into remission. Research on virus therapy began in earnest in the 1990s and has advanced as an immunotherapy for cancer since 2005.

Other names for oncolytic virus therapy include:

  • Oncolytic virotherapy
  • Viral therapy
  • Virotherapy

Researchers are studying the use of oncolytic virus therapy for small-cell lung cancers resistant to immunotherapy alone and for brain tumors.

How to prepare for this immunotherapy

Tell your doctor about any medications you’re taking, whether they’re prescription or over-the-counter. Women should inform their doctor if they’re pregnant or planning to become pregnant.

Questions to ask your doctor:

  • Why are you recommending this treatment at this stage?
  • Where and when will I receive this treatment?
  • How long do the treatment sessions take?
  • How do I prepare for treatment?
  • How will you monitor my cancer and my response to this treatment?

How oncolytic virus therapy is given

Oncolytic virus therapy may be given as an add-on to other treatments you’re receiving. If it’s found to be an appropriate treatment, it may replace other treatments.

Imlygic® should be injected into your tumor. Because not every site may be treated, doctors generally start with the largest lesion and prioritize smaller lesions until all that are able to be treated are targeted. Lesions to be treated are those that are visible, palpable or detectable by ultrasound.

A second treatment is administered three weeks after the first, with additional injections possible every two weeks until no treatable lesions remain.

After treatment, keep your injection sites covered for at least one week. Keep the dressing on longer if the site oozes or weeps.

It’s important to wear gloves when changing or putting on dressings. Be sure to dispose of bandages so that no one comes in contact with them. Use plastic bags to wrap dressings before disposing of them.

Avoid touching or scratching your treatment sites.

Side effects and risks

Trials have shown that most patients respond well to treatment with oncolytic virus therapy and tolerate it. However, some patients experience side effects.

Possible side effects include:

  • Fatigue
  • Chills
  • Fever
  • Nausea
  • Flu-like symptoms
  • Pain at the injection site

Any of these side effects may occur at any time, but they’re most likely within the first three months of treatment.

Other possible reactions include:

  • Rash
  • Worsening psoriasis
  • Cellulitis
  • Vasculitis
  • Difficulty breathing
  • Deep vein thrombosis (DVT)
  • Oral herpes


Avoid oncolytic virus therapy if you:

  • Are pregnant or plan to become pregnant
  • Have leukemia, lymphoma or acquired immunodeficiency syndrome (AIDS) or other human immunodeficiency viruses
  • Are on immunosuppressive therapy
  • Use steroids


Some studies report greater benefit when OVs are given in combination with other immunotherapies, such as an immune checkpoint inhibitor. An immune checkpoint inhibitor is a drug designed to help the immune system fight against cancer.

If oncolytic virus therapy is given before surgery for melanoma, it may enhance your body’s immune response, as well as improve the success of further treatment with a checkpoint inhibitor.

Expert cancer care


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