Abstract
Mismatch repair (MMR) is a highly conserved, fundamental DNA damage repair pathway that maintains genomic fidelity during cell replication. MMR dysregulation contributes to tumor formation by promoting genomic instability thereby increasing the frequency of potentially oncogenic mutational events. Therefore, MMR dysregulation, in its tumor suppressor role, is largely studied in the context of genomic instability and associated response to immune checkpoint blockade therapies. However, a growing body of literature suggests that the impact of MMR dysregulation on tumor phenotypes is more nuanced than a concerted impact on genomic stability. Rather, loss of individual MMR genes promotes distinct cancer-relevant biological phenotypes, and these phenotypes are further modulated by the tissue of tumor origin. Here, we explore relevant literature and review the prognostic and predictive significance of these non-canonical discoveries.