Detection of Microsatellite Instability: State of the Art and Future Applications in Circulating Tumour DNA (ctDNA)

Abstract

Microsatellite instability (MSI) is a molecular scar resulting from a defective mismatch repair system (dMMR) and associated with various malignancies. MSI tumours are characterized by the accumulation of mutations throughout the genome and particularly clustered in highly repetitive microsatellite (MS) regions. MSI/dMMR status is routinely assessed in solid tumours for the initial screening of Lynch syndrome, the evaluation of cancer prognosis, and treatment decision-making. Currently, pentaplex PCR-based methods and MMR immunohistochemistry on tumour tissue samples are the standard diagnostic methods for MSI/dMMR. Other tissue methods such as next-generation sequencing or real-time PCR-based systems have emerged and represent viable alternatives to standard MSI testing in specific settings. The evolution of the standard molecular techniques has offered the opportunity to extend MSI determination to liquid biopsy based on the analysis of cell-free DNA (cfDNA) in plasma. This review aims at synthetizing the standard and emerging techniques used on tumour tissue samples for MSI/dMMR determination. We also provide insights into the MSI molecular techniques compatible with liquid biopsy and the potential clinical consequences for patients with solid cancers.

Mismatch Repair Protein Expression and Microsatellite Instability in Cutaneous Squamous Cell Carcinoma

“…The mismatch repair (MMR) machinery represents an evolutionarily conserved system which is essential for the preservation of cellular DNA homeostasis [ 4 ]. This machinery includes the hMutS heterodimers (MSH2/MSH6 and MSH2/MSH3 complexes) ensuring the specific detection of mispaired nucleotides and small insertion-deletion mutations that are formed during replication/recombination processes [ 2 ] or caused following DNA damage.…”

“…The aforementioned hMutS heterodimers are responsible for the initiation of the DNA repair. Moreover, they recruit the hMutL heterodimers (hMLH1/hPMS2, hMLH1/hPMS1, and hMLH1/hMLH3) in order to catalyse the mispair excision and error-free re-synthesis employing the remaining DNA strand as a template for the DNA polymerase [ 4 ]. Genetic, as well as epigenetic alterations of MMR genes may result in a hypermutability phenotype that is characterized by spontaneous, genome-wide, mutagenesis [ 4 ].…”

“…Moreover, they recruit the hMutL heterodimers (hMLH1/hPMS2, hMLH1/hPMS1, and hMLH1/hMLH3) in order to catalyse the mispair excision and error-free re-synthesis employing the remaining DNA strand as a template for the DNA polymerase [ 4 ]. Genetic, as well as epigenetic alterations of MMR genes may result in a hypermutability phenotype that is characterized by spontaneous, genome-wide, mutagenesis [ 4 ]. In particular, short tandem repeat DNA sequences, also called microsatellites are affected, making individuals more susceptible to malignancies.…”

“…In this context, it is of significance that the prognosis of most malignancies with high-level microsatellite instability (MSI-H) and deficient MMR (dMMR) is relatively good, in particular when treated with ICIs [ 4 ]. However, there exist relatively sparse and conflicting data on MSI-H/dMMR in cutaneous malignancies.…”

Identification of a Genome Instability-Associated LncRNA Signature for Prognosis Prediction in Colon Cancer

“…However, the role of somatic mutations in the carcinogenesis of colon cancer has not been largely explored. Microsatellite instability (MSI), caused by a defective mismatch repair system, is characterized by the widespread mutation throughout the genome and particularly clustered in highly repetitive microsatellite region ( Dai et al, 2021 ; Gilson et al, 2021 ), suggesting that MSI could be used as genome instability index for cancer. Recently, the presence of MSI was demonstrated as a predictive biomarker for immunotherapy and prognosis ( Li K. et al, 2020 ; Zhu et al, 2021 ).…”