Imlygic (talimogene laherparepvec; Amgen), a genetically modified oncolytic viral therapy, has been approved for the local treatment of unresectable cutaneous, subcutaneous and nodal lesions in patients with melanoma recurrent after initial surgery. This is the first oncolytic viral therapy approved by the FDA based on therapeutic benefit demonstrated in a pivotal clinical trial.

The approval was based on a Phase 3, multicenter, open-label, randomized study comparing Imlygic to granulocyte-macrophage colony-stimulating factor (GM-CSF) in 436 patients with advanced melanoma (Stage IIIB, IIIC, or IV) that was not surgically resectable. The primary endpoint of the study was durable response rate (DRR), defined as the percent of patients with complete response (CR) or partial response (PR) maintained continuously for a minimum of six months. In the study, more patients treated with Imlygic achieved a durable response compared to those treated with GM-CSF (16.3% vs. 2.1%; respectively). In the group that experienced a durable response, 29.1% had a durable CR and 70.8% had a durable PR. In the Imlygic arm, the mean time to response was 4.1 months (range: 1.2 to 16.7 months).

Imlygic is a genetically modified herpes simplex virus type 1 injected directly into tumors where it replicates inside tumors and produces the immune stimulatory protein GM-CSF.  Imlygic causes lysis of tumors, followed by release of tumor-derived antigens, which together with virally derived GM-CSF may promote an antitimor immune response.  The exact mechanism of action, however, is unknown.

Because Imlygic is a live, attenuated herpes simplex virus, it can cause life-threateneing disseminated herpetic infection in immunocompromised patients and is therefore contraindicated in this patient population.  Imlygic should not be be administered to patients with a history of primary or acquired immunodeficient states, leukemia, lymphoma, AIDS, other clinical manifestations of infection with human immunodeficiency viruses, and those on immunosuppressive therapy; it should also not be administered to pregnant patients.

Amgen plans on making Imlygic available to patients within a week. The product will be available in single-use vials in two strengths:  106 (1 million) PFU per mL and 108 (100 million) PFU per mL.

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