Colorectal Cancers and Microsatellite Instability

Colorectal cancer (CRC) is a multifactorial disease arising from the complex interplay between genetic predisposition and environmental influences. Despite its widespread incidence globally, CRC demonstrates favorable prognostic outcomes when detected at an early stage. Microsatellite instability (MSI) is a common molecular abnormality associated with colorectal tumorigenesis. This review provides a comprehensive analysis of the molecular mechanisms, clinical implications, therapeutic approaches, and immune system interactions in MSI-associated CRC (MSI-CRC). Molecular changes include DNA slippage, dysfunction in the DNA mismatch repair (dMMR) system, and genetic/epigenetic factors that contribute to MSI. Clinically, MSI-CRC is characterized by distinct phenotypic features, including associations with Lynch syndrome, specific diagnostic methodologies, and prognostic relevance. The therapeutic landscape highlights the promising efficacy of immunotherapies and targeted treatments, particularly in dMMR-MSI-H-CRC. Immune dynamics within the tumor microenvironment (TME) reveal patterns of immune infiltration, immune evasion strategies, and opportunities to enhance the effectiveness of immunotherapy. Understanding these interrelated aspects is critical for developing tailored therapeutic strategies and improving patient outcomes in MSI-CRC.