Mismatch repair (MMR) system is one form of DNA repair mechanisms, which plays an important role in rectifying the mismatch of base pairs, reducing gene mutations and keeping genome stability. Abnormal expression of MMR regulated by miRNA is closely related to the development of colon cancer. Functional defects of MMR (dMMR) with particular clinical characteristics can be used as a potential prognostic and predictive biomarker. This article reviews the relation between MMR system, miRNA and colon cancer.
Colonic Neoplasms ; genetics ; DNA Mismatch Repair ; Humans ; MicroRNAs ; genetics ; Mutation ; Prognosis

OBJECTIVE: To explore the clinicopathological features and types of genic mutations in DNA mismatch repair (MMR) in colorectal cancer (CRC). METHODS: Immunohistochemistry was used to determine the expression of MMR proteins in 1394 patients with CRC, and PCR-capillary electrophoresis (PCR-CE) was used to detect microsatellite instability (MSI) in 106 cases of defective MMR (dMMR), 46 cases of proficient MMR (pMMR) with heterogeneous expression and 147 randomly selected cases of pMMR. The relationship between the expressions of MMR proteins and the clinicopathological features of the patients was evaluated. The consistency between the results of immunohistochemistry and PCR-CE was assessed. RESULTS: Immunohistochemical staining showed an incidence of dMMR of 7.6% in the patients. The main type of dMMR was co-deletion of MLH1 and PMS2, accounting for 55.7% of the total dMMR cases. The deletion of MMR proteins was significantly correlated with the patients' age, tumor location, tumor size, gross type, histological type, degree of differentiation, lymph node status and TNM stage ( CONCLUSIONS The main type of dMMR is co-deletion of MLH1 and PMS2 in patients with colorectal cancer. dMMR colorectal cancer has typical clinicopathological features and a lower incidence in China than in Western countries. The results of immunohistochemistry and PCR-CE are highly consistent for detecting dMMR in colorectal cancer patients.
China ; Colorectal Neoplasms/genetics* ; DNA Mismatch Repair/genetics* ; Humans ; Microsatellite Instability

Objective: To investigate the relationship between the expression of four mismatch repair proteins (MLH1, MSH2, MSH6 and PMS2) and NTRK genetic fusions in colorectal cancer. Methods: The paraffin-embedded tissue blocks of 830 cases of colorectal cancer were collected at the Affiliated Drum Tower Hospital, Nanjing University Medical School, China, from 2015 to 2019. Immunohistochemical and fluorescence in situ hybridization(FISH) method were used respectively to detect the expression of mismatch repair proteins and the break-apart of NTRKs; and the relationship between the expression of mismatch repair proteins and the NTRK genetic fusions was analyzed. Results: The overall mismatch repair protein deficiency (dMMR) rate was 9.88% (82/830), the mismatch repair proteins proficiency (pMMR) rate was 90.12%(748/830). The total deficiency rate of MLH1 protein was 9.04% (75/830), hPMS2 protein deficiency rate was 9.04% (75/830), MSH2 protein deficiency rate was 2.53% (21/830), MSH6 protein deficiency rate was 4.10% (34/830), the deficiency rate of synchronous MLH1 and PMS2 were 8.67% (72/830) and the deficiency rate of synchronous MSH2 and MSH6 were 2.17% (18/830). The dMMR group was associated with tumor location, different histological subgroups, tumor differentiation, AJCC stage and N stage (P<0.05). There were six cases (7.32%) carrying NTRK fusion by FISH among the 82 cases of dMMR, but only seven cases (0.94%) carrying NTRK fusion among the 748 cases of PMMR. The NTRKs translocation by FISH in all 13 cases were further confirmed by next generation sequencing. Among the clinicopathological characteristics, only differentiation showed significant difference between NTRK fusion positive and negative groups (P<0.05). More importantly, NTRK fusion was enriched in dMMR group (7.32% vs. 0.94%). Conclusion: In dMMR colorectal cancer group, the prevalence of NTRK fusion is higher than that in pMMR group.
Colonic Neoplasms ; Colorectal Neoplasms/genetics* ; DNA Mismatch Repair/genetics* ; Humans ; In Situ Hybridization, Fluorescence ; Mismatch Repair Endonuclease PMS2/metabolism* ; MutL Protein Homolog 1/metabolism* ; MutS Homolog 2 Protein/metabolism*

Hereditary non-polyposis colorectal cancer (HNPCC) is an autosomal dominantly inherited disease associated with germ-line mutations in mismatch repair genes and microsatellite instability. This article reviews the molecular biology and clinical pathology of HNPCC.
Colorectal Neoplasms, Hereditary Nonpolyposis ; diagnosis ; genetics ; pathology ; DNA Mismatch Repair ; Humans ; Microsatellite Instability

Colorectal Neoplasms ; genetics ; Colorectal Neoplasms, Hereditary Nonpolyposis ; metabolism ; DNA Mismatch Repair ; Humans ; Microsatellite Instability

Immunotherapy has become an important treatment option for microsatellite instability-high (MSI-H) and mismatch repair deficient (dMMR) colorectal cancer. From late-line to first-line treatment, and even in neoadjuvant setting for early stage colorectal cancer, promising efficacy was observed with immunotherapy. In microsatellite stability (MSS) or mismatch repair proficient (pMMR) colorectal cancer, the researches of neoadjuvant immunotherapy have been conducted constantly. This paper focuses on the recent researches and progress of neoadjuvant immunotherapy for MSS or pMMR colorectal cancer. Neoadjuvant immunotherapy alone led to a good pathological response in a subset of patients. Studies of induction or consolidation immunotherapy before or after neoadjuvant chemoradiotherapy or concurrent immunotherapy during radiotherapy showed higher pathological complete remission (pCR) rates as compared to standard chemoradiotherapy. Studies on sequential dual immunotherapy after radiochemotherapy and targeted therapy combined with neoadjuvant immunotherapy are ongoing. At present, most of these are pilot studies with small sample size. More researches and long-term follow-up are needed to prove the efficacy of neoadjuvant immunotherapy in MSS or pMMR colorectal cancer.
Colorectal Neoplasms/therapy* ; DNA Mismatch Repair/genetics* ; Humans ; Immunotherapy ; Microsatellite Repeats ; Neoadjuvant Therapy

BACKGROUND: Microsatellite instability (MSI) is a key biomarker for cancer immunotherapy and prognosis. Integration of MSI testing into a next-generation-sequencing (NGS) panel could save tissue sample, reduce turn-around time and cost, and provide MSI status and comprehensive genomic profiling in single test. We aimed to develop an MSI calling model to detect MSI status along with the NGS panel-based profiling test using tumor-only samples. METHODS: From January 2019 to December 2020, a total of 174 colorectal cancer (CRC) patients were enrolled, including 31 MSI-high (MSI-H) and 143 microsatellite stability (MSS) cases. Among them, 56 paired tumor and normal samples (10 MSI-H and 46 MSS) were used for modeling, and another 118 tumor-only samples were used for validation. MSI polymerase chain reaction (MSI-PCR) was performed as the gold standard. A baseline was built for the selected microsatellite loci using the NGS data of 56 normal blood samples. An MSI detection model was constructed by analyzing the NGS data of tissue samples. The performance of the model was compared with the results of MSI-PCR. RESULTS: We first intersected the target genomic regions of the NGS panels used in this study to select common microsatellite loci. A total of 42 loci including 23 mononucleotide repeat sites and 19 longer repeat sites were candidates for modeling. As mononucleotide repeat sites are more sensitive and specific for detecting MSI status than sites with longer length motif and the mononucleotide repeat sites performed even better than the total sites, a model containing 23 mononucleotide repeat sites was constructed and named Colorectal Cancer Microsatellite Instability test (CRC-MSI). The model achieved 100% sensitivity and 100% specificity when compared with MSI-PCR in both training and validation sets. Furthermore, the CRC-MSI model was robust with the tumor content as low as 6%. In addition, 8 out of 10 MSI-H samples showed alternations in the four mismatch repair genes ( MLH1 , MSH2 , MSH6 , and PMS2 ). CONCLUSION MSI status can be accurately determined along the targeted NGS panels using only tumor samples. The performance of mononucleotide repeat sites surpasses loci with longer repeat motif in MSI calling.
Humans ; Microsatellite Instability ; Colorectal Neoplasms/diagnosis* ; Microsatellite Repeats/genetics* ; DNA Mismatch Repair

OBJECTIVETo study hMSH2 genetic polymorphism in southern Chinese Han population.

METHODSThe basic materials and blood samples from 163 southern Chinese were collected. The mutations of exon 6 and exon 7 of hMSH2 gene were investigated by PCR-SSCP, followed by DNA sequencing.

RESULTSFragments of 250 bp including exon 6 and fragments of 323 bp including exon 7 of hMSH2 gene were amplified by multiple PCR. The allele frequencies of C18, A82 and B39 type mutations were 0.0184, 0.0031, 0.0031, respectively. The gene frequencies and gene type frequencies of three polymorphism sites in normal population accorded with Hardy-Weinberg equilibrium (P>0.05). The heterozygosity of C18 type mutation (0.0361) was the highest.

CONCLUSIONThere were three polymorphism sites in exon 7 of hMSH2 gene in southern Chinese Han population, among which the genotype frequency of C18 type was the highest, suggesting that C18 type mutation be a useful genetic mark.

Asian Continental Ancestry Group ; genetics ; Base Pair Mismatch ; DNA Ligase ATP ; DNA Ligases ; genetics ; DNA Mismatch Repair ; genetics ; physiology ; DNA Repair Enzymes ; genetics ; Exons ; genetics ; Female ; Humans ; Male ; Microsatellite Repeats ; genetics ; Middle Aged ; Polymorphism, Genetic

OBJECTIVETo evaluate the sensitivity and specificity of immunohistochemical (IHC) staining of DNA mismatch repair (MMR) protein for the screening of microsatellite instability (MSI) colorectal cancer (CRC).

METHODSA total of 255 CRC cases were studied, including 140 cases of routine paraffin-embedded tissue samples and 115 cases constructed on tissue microarray. Expressions of 4 MMR proteins including MHL1, MSH2, MSH6 and PMS2 were investigated by IHC. Negative protein expression was defined as complete absence of nuclear staining within tumor cells in the presence of positively labeled internal non-neoplastic cells. Focal staining was defined as the presence of staining in < 5% of the tumor cells. CRCs showing negative staining for any MMR proteins were interpreted as MMR deficient tumors. PCR-genescan MSI analysis was performed in each case by a five marker panel including Bat26, Bat25, NR-21, NR-24 and MONO-27.

RESULTSAmong the 140 CRCs with routine formalin-fixed paraffin embedded tissue sections, concordance rate between IHC and PCR-genescan was 98.6% (138/140), the sensitivity and specificity of IHC in detecting MSI tumors were 94.9% (37/39) and 100.0% (101/101), respectively. The 2 disconcordant cases showed focal staining in at least one of the MMR proteins but were confirmed to be MSI-H CRCs by PCR-genescan assay. On tissue microarray, 91.3% (105/115) of the cases had informative results. The concordance rate between IHC and PCR-genescan was 100.0% (105/105). Both the specificity and sensitivity of IHC in detecting MSI tumors on available tissue microarray samples were 100.0%. Ten cases were inclusive due to the presence of negative stains of MMR proteins in both the tumor and internal control cells.

CONCLUSIONSDetection of 4 MMR proteins expression by IHC is reliable for identifying MSI CRCs and is recommended for routine practice. Tumors with focal MMR protein staining are highly suspected for the presence of MSI-H and PCR-genescan based MSI analysis should be performed to confirm.

Colorectal Neoplasms ; genetics ; DNA Mismatch Repair ; DNA-Binding Proteins ; deficiency ; genetics ; Humans ; Immunohistochemistry ; Microsatellite Instability ; Polymerase Chain Reaction ; Sensitivity and Specificity

OBJECTIVETo analyze the clinical and pathological features of patients with hereditary nonpolyposis colorectal cancer (HNPCC).

METHODSThe data of 8 HNPCC pedigrees according with Amsterdam standard II were collected and their pedigree trees were generated.

RESULTSThe morbidity of HNPCC was 1.59%. Thirty-one patients were found in the 8 HNPCC pedigrees including 25 with colorectal cancer and 6 with extraintestinal tumors. The 8 probands consisted of 6 female and 2 male patients, among whom 4 were younger than 40 years old, 2 had lesions in the right colon, 3 in the left colon, and 3 in the rectum. The tumors were histologically identified mainly as highly to moderately differentiated adenocarcinoma; all the patients were free of lymph node or distant metastasis. Of the 8 probands, 5 had abnormal expression of MMR protein and only 1 had normal expression.

CONCLUSIONThe HNPCC probands are characterized by early onset at a young age and high differentiation of the tumor. The members of the pedigrees show a high incidence of the malignancies, and regular examination and timely treatment can be effective in preventing the tumor occurrence and reducing the mortality. Detection of MMR gene mutation can be a crucial approach to raising the diagnostic rate of HNPCC.

Adult ; Aged ; Colorectal Neoplasms, Hereditary Nonpolyposis ; genetics ; pathology ; DNA Mismatch Repair ; genetics ; Female ; Humans ; Male ; Middle Aged ; Pedigree