Late Breaking Abstract – ASCO 2024: Sustained Improvement in Relapse Free Survival with Personalized mRNA Cancer Vaccine plus KEYTRUDA® in Resected High Risk Melanoma

SUMMARY: The American Cancer Society estimates that for 2024, about 100,640 new cases of melanoma of the skin will be diagnosed in the United States and 8,290 people are expected to die of the disease. The rates of melanoma have been rising rapidly over the past few decades, but this has varied by age. Surgical resection with a curative intent is the standard of care for patients with early stage melanoma.

Patients with resected Stage IIB/C disease comprise a significant group of patients at significant risk of recurrence. Patients with Stage IIB disease have primary tumors that are more than 2 mm, and 4 mm or less in thickness, with ulceration (T3b), or more than 4 mm in thickness without ulceration (T4a). Patients with Stage IIC disease have primary tumors more than 4 mm in thickness with ulceration (T4b). Although Stage II melanoma is less advanced than Stage III, the 5-year risk of recurrence in patients with Stage IIB or Stage IIC disease without adjuvant therapy is approximately 35% and 50% respectively. The 5-year Melanoma-Specific Survival (MSS) rates for patients with Stage IIB/IIC disease are similar to those for Stage IIIA, Stage IIIB and Stage IIIC disease.

Immune Checkpoint Inhibitors are the standard of care adjuvant treatment for high-risk resected melanoma. In the KEYNOTE-054 trial, the 5-year Relapse Free Survival (RFS) with adjuvant Pembrolizumab (KEYTRUDA®) was 55.4% versus 38.3% with placebo. In the CHECKMATE-238 trial, the 4-year RFS rate was of 51.7% for Nivolumab (OPDIVO®) versus 41.2% for ipilimumab (YERVOY®). Given the high relapse rates with the present adjuvant melanoma therapies, there is an unmet clinical need.

Pembrolizumab is a fully humanized, Immunoglobulin G4, anti-PD-1, monoclonal antibody, that binds to the PD-1 receptor and blocks its interaction with ligands PD-L1 and PD-L2. By doing so, it unleashes the tumor-specific effector T cells, and is thereby able to undo PD-1 pathway-mediated inhibition of the immune response.

mRNA-4157 (V940) is a novel messenger RiboNucleic Acid (mRNA)-based individualized neoantigen therapy consisting of a single synthetic mRNA coding for up to 34 neoantigens, that is designed and produced based on the unique mutational signature of the DNA sequence of the patients tumor. Individualized neoantigen therapies are designed to prime the immune system so that a patient can generate a tailored antitumor response specific to their tumor mutation signature. mRNA-4157 (V940) was designed to stimulate an immune response by generating specific T cell responses based on the unique mutational signature of a patients tumor. Early clinical studies demonstrated that combining mRNA-4157 (V940) with Pembrolizumab may potentially provide an additive benefit and enhance T cell-mediated destruction of tumor cells.

KEYNOTE-942 is an ongoing randomized, open-label, Phase IIb trial, designed to evaluate the efficacy and safety of mRNA-4157, an individualized neoantigen therapy, in combination with Pembrolizumab, in patients with completely resected high-risk Stage III/IV cutaneous melanoma. This study included 157 patients who were randomly assigned (2:1) to receive mRNA-4157 in combination with Pembrolizumab (N=107) or Pembrolizumab alone (N=50). The vaccine was administered 1 mg every three weeks for a total of nine doses, and Pembrolizumab was given at 200 mg IV every three weeks for up to 18 cycles (approximately one year). All patients had tumor sample (Formalin Fixed Paraffin Embedded-FFPE) available for Next Generation Sequencing and patients were stratified by disease stage. mRNA-4157 was successfully prepared for more than 99% of patients in the combination arm. The median patient age was 62 years and 84% of patients had Stage IIIC disease. Approximately 64% of patients were PD-L1 positive and 74% had high Tumor Mutational Burden-TMB (10 or more mutations/Mb) in the combination treatment group, whereas 54% were PD-L1 positive and 60% had high TMB in the single agent Pembrolizumab group, respectively. HLA genotyping was performed to explore associations between specific HLA alleles and treatment response. Additionally, subgroup analyses were conducted based on TMB, PD-L1 expression, and circulating tumor DNA (ctDNA) status.

The Primary endpoint was Relapse Free Survival (RFS), defined as the time from first dose of Pembrolizumab until the date of first recurrence (local, regional, or distant metastasis), a new primary melanoma, or death from any cause. Secondary endpoints included Distant Metastasis-Free Survival and Safety. Exploratory endpoints included distribution of TMB expression in baseline tumor samples across study arms and their association with the primary RFS endpoint.

At a median follow up of 23 months for the mRNA-4157/V940 plus Pembrolizumab group, and 24 months for Pembrolizumab alone group, the Relapse Free Survival at 18 months was 78.6% for the immunotherapy combination versus 62.2% for Pembrolizumab alone (HR=0.56; P=0.0266), and this equated to a 44% reduction in the risk of recurrence or death with 2 years of follow-up. mRNA-4157/V940 and Pembrolizumab combination treatment demonstrated an improvement in RFS, irrespective of PD-L1 status and TMB status.

In the recent data presented at ASCO 2024, with an additional year of planned follow-up, at a median of approximately 34.9 months, the combination of mRNA-4157 and Pembrolizumab demonstrated a significant clinically meaningful and durable improvement in RFS, the Primary endpoint of the study, compared to Pembrolizumab alone. The risk of recurrence or death was reduced by 49% (HR=0.51; P=0.019), compared to Pembrolizumab monotherapy. The 2.5-year RFS rate for the combination group was 74.8% compared to 55.6% in the Pembrolizumab alone group. The RFS improvement was observed across subgroups irrespective of TMB and PD-L1 levels.

The combination therapy also showed a meaningful improvement in Distant Metastasis-Free Survival, which was a key Secondary endpoint, compared to Pembrolizumab alone (HR=0.38; P=0.015). This represented a 62% reduction in the risk of developing distant metastases or death compared to Pembrolizumab alone.

While not formally tested as a Primary endpoint, Overall Survival trended favorably with the combination therapy, with a 2.5-Year OS Rate of 96.0% for combination versus 90.2% for Pembrolizumab alone (HR=0.425).

The safety profile of mRNA-4157 in combination with Pembrolizumab was consistent with previous analyses and the common adverse events were fatigue (60.6%), injection site pain (56.7%), and chills (49.0%). Grade 3 or higher adverse events occurred in 25% of patients receiving combination therapy and 18% in the Pembrolizumab alone group. Immune-related adverse events were reported by approximately 37.5% of patients in the combination group and 36% in the Pembrolizumab alone group, with no new safety signals identified.

The KEYNOTE-942 trial demonstrated that mRNA-4157 in combination with Pembrolizumab significantly improved Recurrence-Free Survival and Distant Metastasis-Free Survival in patients with resected high-risk Stage III/IV melanoma, compared to Pembrolizumab alone. These findings suggest a potential benefit across various patient subgroups based on TMB, PD-L1 expression, and ctDNA status. The safety profile was manageable and consistent with expectations for both treatments. Based on these positive results, further investigation in the Phase III INTerpath-001 trial is underway to validate these findings and potentially transform the adjuvant treatment landscape for melanoma patients.

Individualized neoantigen therapy mRNA-4157 (V940) plus pembrolizumab in resected melanoma: 3-year update from the mRNA-4157-P201 (KEYNOTE-942) trial.Weber JS, Khattak MA, Carlino MS, et al. J Clin Oncol 42, 2024 (suppl 17; abstr LBA9512). DOI 10.1200/JCO.2024.42.17_suppl.LBA9512