The safety and efficacy of intralesional injections of IMLYGIC compared with subcutaneously administered GM-CSF was evaluated in a multicenter, open-label, randomized clinical study in patients with stage IIIB, IIIC, and IV melanoma that was considered to be not surgically resectable. IMLYGIC was injected into cutaneous, subcutaneous, or nodal melanoma lesions and was not injected into visceral lesions. Previous systemic treatment for melanoma was allowed. Patients with active cerebral metastases, bony metastases, extensive visceral disease, primary ocular or mucosal melanoma, evidence of immunosuppression, or receiving treatment with a systemic antiherpetic agent were excluded from the study.

The study included 250 (57%) men and 186 (43%) women. The mean age was 63 (range: 22 to 94) years. Most patients (98%) were white. Seventy percent (70%) of patients had baseline Eastern Cooperative Oncology Group (ECOG) performance status of zero. Seventy percent (70%) of patients had stage IV disease (27% M1a; 21% M1b; and 22% M1c), and 30% had stage III disease. Fifty-three percent (53%) of patients had received prior therapy for melanoma (other than or in addition to surgery, adjuvant therapy, or radiation), and 58% were seropositive for wild-type HSV-1 at baseline.

A total of 436 patients were randomized to receive either IMLYGIC (n = 295) or GM-CSF (n = 141). IMLYGIC was administered by intralesional injection at an initial concentration of 106 (1 million) PFU per mL on Day 1, followed by a concentration of 108 (100 million) PFU per mL on Day 21 and every 2 weeks thereafter, at a dose of up to 4 mL per visit. GM-CSF was administered subcutaneously in 28-day cycles, i.e., 125 µg/m2 daily for 14 days followed by 14 days without GM-CSF administration.

Patients were to be treated for at least 6 months or until there were no injectable lesions. During this period, treatment could continue despite an increase in size in existing lesion(s) and/or development of new lesion(s), unless the patient developed intolerable toxicity or the investigator believed that it was in the best interest of the patient to stop treatment or to be given other therapy for melanoma. After 6 months of treatment, patients were to continue treatment until clinically relevant disease progression (i.e., disease progression associated with a decline in performance status and/or alternative therapy was required in the opinion of the investigator), up to 12 months. Patients experiencing a response at 12 months after the start of treatment could continue treatment for up to an additional 6 months, unless there were no remaining injectable lesions or disease progression. All patients were to be followed for survival status for at least 36 months.

The major efficacy outcome 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 6 months. Tumor responses were determined according to World Health Organization (WHO) response criteria modified to allow patients who developed new lesions or disease progression of existing lesions to continue the treatment and be evaluated later for tumor response.

The DRR was 16.3% in the IMLYGIC arm and 2.1% in the GM-CSF arm in the overall study population. The unadjusted relative risk was 7.6 (95% CI: 2.4, 24.1), with a p-value < 0.0001. The median time to response was 4.1 (range: 1.2 to 16.7) months in the IMLYGIC arm.

There was no statistically significant difference in overall survival (OS) between the IMLYGIC and the GM-CSF arms. The median OS in the overall study population was 22.9 months in the IMLYGIC arm and 19.0 months in the GM-CSF arm (p = 0.116).