Microsatellite instability as a predictive factor for immunotherapy in malignant melanoma

Area of Science:

• Oncology
• Immunology
• Genetics

Background:

• Immunotherapy shows promise for metastatic melanoma but lacks predictive biomarkers.
• Microsatellite instability (MSI), a DNA mismatch repair deficiency, is emerging as a potential predictive marker.
• Tumor immunogenicity, influenced by mutational heterogeneity, is key to immunotherapy success, with melanoma showing high somatic mutations.

Purpose of the Study:

• To investigate microsatellite instability (MSI) as a predictive biomarker for immunotherapy response in malignant melanoma.
• To explore the rationale for using immunotherapy in MSI-positive melanomas based on immunogenicity and neo-antigen load.

Main Methods:

• Review of existing evidence linking MSI status to tumor immunogenicity and treatment outcomes.
• Analysis of MSI's association with immune cell infiltration and inhibitory factors, drawing parallels from colorectal cancer studies.

Main Results:

• MSI in colorectal cancer correlates with increased antitumor lymphocytes (CD3+, CD8+, CD45RO+, T-bet+) and decreased inhibitory factors (Foxp3, IL-6, IL-17, TGF-β).
• MSI tumors accumulate somatic mutations, leading to high neo-antigen levels and potential resistance to conventional therapies, suggesting immunotherapy suitability.

Conclusions:

• The MSI phenotype in malignant melanoma may help identify patients likely to benefit from immunotherapy.
• MSI status presents a promising avenue for personalizing melanoma treatment strategies, optimizing immunotherapy efficacy.