Microsatellite instability at a tetranucleotide repeat in type I endometrial carcinoma

Elevated Microsatellite Alterations at Selected Tetranucleotide Repeats (EMAST) in Penile Squamous Cell Carcinoma-No Evidence for a Role in Carcinogenesis

Penile squamous cell carcinoma (pSCC) is a rare malignancy with a global incidence ranging from 0.1 to 0.7 per 100,000 males. Prognosis is generally favorable for localized tumors, but metastatic pSCC remains challenging, with low survival rates. The role of novel biomarkers, such as tumor mutational burden (TMB) and microsatellite instability (MSI), in predicting the response to immune checkpoint inhibitors (ICIs) has been investigated in various cancers. However, MSI has not been observed in pSCC, limiting immunotherapy options for this patient subgroup. Elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) are a distinct form of genomic instability associated with deficient MSH3 expression, which has been proposed as a potential biomarker in several cancers. This study investigates EMAST and MSH3 expression in a cohort of 78 pSCC cases using PCR, fragment analysis and immunohistochemistry. For the detection of EMAST, the stability of five microsatellite markers (D9S242, D20S82, MYCL1, D8S321 and D20S85) was analyzed. None of the cases showed an instability. As for MSH3 immunohistochemistry, all analyzable cases showed retained MSH3 expression. These results strongly suggest that neither EMAST nor MSH3 deficiency is involved in the carcinogenesis of pSCC and do not represent reliable predictive biomarkers in this entity. Furthermore, these findings are in full agreement with our previous study showing a very low frequency of MSI and further support the thesis that EMAST and MSI are strongly interconnected forms of genomic instability. Further research is needed to explore novel therapeutic targets and predictive biomarkers for immunotherapy in this patient population.

The Role of Immunohistochemistry Markers in Endometrial Cancer with Mismatch Repair Deficiency: A Systematic Review

The objective of this systematic review was to summarize our current knowledge of the role of immunohistochemistry (IHC) markers for identifying mismatch repair-deficient (MMRd) tumors in endometrial cancer (EC). Identification of MMRd tumors, which occur in 13% to 30% of all ECs, has become critical for patients with colorectal and endometrial cancer for therapeutic management, clinical decision making, and prognosis. This review was conducted by two authors applying the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines using the following terms: “immunohistochemistry and microsatellite instability endometrial cancer” or “immunohistochemistry and mismatch repair endometrial cancer” or “immunohistochemistry and mismatch repair deficient endometrial cancer”. Among 596 retrieved studies, 161 fulfilled the inclusion criteria. Articles were classified and presented according to their interest for the diagnosis, prognosis, and theragnostics for patients with MMRd EC. We identified 10, 18, and 96 articles using IHC expression of two, three, or four proteins of the MMR system (MLH1, MSH2, MHS6, and PMS2), respectively. MLH1 promoter methylation was analyzed in 57 articles. Thirty-four articles classified MMRd tumors with IHC markers according to their prognosis in terms of recurrence-free survival (RFS), overall survival (OS), stage, grade, and lymph node invasion. Theragnostics were studied in eight articles underlying the important concentration of PD-L1 in MMRd EC. Even though the role of IHC has been challenged, it represents the most common, robust, and cheapest method for diagnosing MMRd tumors in EC and is a valuable tool for exploring novel biotherapies and treatment modalities.

EMAST frequency in colorectal cancer: a meta-analysis and literature review

Aim: The prognostic and predictive value of Elevated Microsatellite Alterations at Selected Tetranucleotide (EMAST) has been reported in colorectal cancer (CRC). The prevalence of EMAST in CRC varied across the literature. We conducted a meta-analysis to determine the prevalence of EMAST in CRC. Materials & methods: Three international databases including PubMed, ISI and Scopus were searched to identify related articles that described the frequency of EMAST. Results: Analysis was performed on 16 eligible studies including 4922 patients. The overall EMAST prevalence among CRCs patients was 33% (95% CI: 23-43%, I2 = 98%). Conclusion: This study indicated that approximately a third of the CRC patients are diagnosed with EMAST, hereupon EMAST as a prognostic and predictive biomarker should be more studied clinically.

Diagnostic Accuracy of Immunohistochemistry for Mismatch Repair Proteins as Surrogate of Microsatellite Instability Molecular Testing in Endometrial Cancer

Microsatellite instability (MSI) defines one of the four molecular groups of endometrial carcinoma identified by The Cancer Genome Atlas (TCGA). Immunohistochemistry for mismatch repair (MMR) proteins (MLH1, MSH2, MSH6, PMS2) has been proposed as a widely applicable technique to identify this group in the common practice. However, the diagnostic accuracy of such approach has never been calculated. We aimed to assess: 1) the diagnostic accuracy of MMR proteins immunohistochemistry as surrogate of MSI molecular testing in endometrial carcinoma; 2) whether a combination of only two MMR proteins may be used as a still cheaper test. A systematic review and meta-analysis of was performed by searching electronic databases from their inception to September 2019. All studies assessing endometrial carcinoma with both MMR proteins immunohistochemistry and MSI molecular testing were included. Diagnostic accuracy was assessed as sensitivity, specificity, positive and negative likelihood ratios (LR+, LR-), diagnostic odds ratio (DOR) and area under the curve (AUC) on SROC curves. A subgroup analysis was performed for a combination of only two MMR proteins (MLH1-MSH2 vs MSH6-PMS2). Ten studies with 3097 patients were included. Out of these, 1110 were suitable for the meta-analysis. Immunohistochemistry for all the four MMR proteins showed sensitivity = 0.96, specificity = 0.95, LR + =17.7, LR- = 0.05, DOR = 429.77, and high diagnostic accuracy (AUC = 0.988). The combination of MLH1 and MSH2 showed sensitivity = 0.88, specificity = 0.96, LR + =22.36, LR- = 0.15, DOR = 200.69, and high diagnostic accuracy (AUC = 0.9838). The combination of MSH6 and PMS2 showed the same results as the complete panel of four MMR proteins. In conclusion, MMR proteins immunohistochemistry is a highly accurate surrogate of MSI molecular testing in endometrial carcinoma. A combination of MSH6 and PMS2 may allow reducing the cost without decrease in the diagnostic accuracy.

Elevated Microsatellite Alterations at Selected Tetranucleotides (EMAST) Is Not Attributed to MSH3 Loss in Stage I-III Colon cancer: An Automated, Digitalized Assessment by Immunohistochemistry of Whole Slides and Hot Spots

INTRODUCTION

EMAST is a poorly understood form of microsatellite instability (MSI) in colorectal cancer (CRC) for which loss of MSH3 has been proposed as the underlying mechanism, based on experimental studies. We aimed to evaluate whether MSH3 loss is associated with EMAST in CRC.

METHODS

A consecutive cohort of patients with stage I-III CRC. Digital image analysis using heatmap-derived hot spots investigated MSH3 expression by immunohistochemistry. Fragment analysis of multiplex PCR was used to assess MSI and EMAST, and results cross-examined with MSH3 protein expression.

RESULTS

Of 152 patients, EMAST was found in 50 (33%) and exclusively in the colon. Most EMAST-positive cancers had instability at all 5 markers, and EMAST overlapped with MSI-H in 42/50 cases (84%). The most frequently altered tetranucleotide markers were D8S321 (38.2% of tumors) and D20S82 (34.4%). Subjective evaluation of MSH3 expression by IHC in tumor found ≤10% negative tumor cells in all samples, most being ≤5% negative. Digital analysis improved the detection but showed a similar spread of MSH3 loss (range 0.1-15.7%, mean 2.2%). Hotspot MSH3 negativity ranged between 0.1 to 95.0%, (mean 8.6%) with significant correlation with the whole slide analysis (Spearman's rho=0.677 P<.001). Loss of MSH3 expression did not correlate with EMAST.

CONCLUSIONS

In a well-defined cohort of patients with CRC, loss of MSH3 was not associated with EMAST. Further investigation into the mechanisms leading to EMAST in CRC is needed.

MSI-L/EMAST is a predictive biomarker for metastasis in colorectal cancer patients

BACKGROUND

Microsatellite instability (MSI) is a prognostic marker in colorectal cancer (CRC). The biological significance of MSI-low (MSI-L) phenotype and its differences with microsatellite stable (MSS) phenotype remains unclear. The aim of this study is indicating the role of mononucleotide repeat in identifying MSI-L and revealing the association of MSI-L with elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) and oncologic outcome in CRC patients.

METHODS

MSI and EMAST status were analyzed using three quasimonomorphic panel (BAT-25, BAT-26, and NR-27) and five tetranucleotide repeats (D20S82, D20S85, D9S242, D8S321, and MYCL1), respectively, by capillary electrophoresis method without the need to fluorescent primers. The associations of MSI status with clinicopathological features, EMAST status, metastasis, and overall survival (OS) were investigated.

RESULTS

Among 159 CRC patient 22.0% were MSI-H, 40.3% were MSS, 37.7% were MSI-L, and 41.5% showed EMAST + phenotype. MSI-L were associated with advanced stages, EMAST⁺ tumors and worse OS ( p ≤ 0.001). Metastasis was relatively common in MSI-L/EMAST ⁺ CRCs and BAT-25 were the most unstable marker in these tumors.

CONCLUSIONS

MSI-L tumors have different clinicopathological features from MSS and MSI-H tumors. The MSI-L phenotype is a worse prognostic biomarker in CRC and when accompanied by EMAST could be a predictor for metastasis.

Prevalence of elevated microsatellite alterations at selected tetranucleotide repeats in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) prognosis remains poor even after complete resection owing to no valuable biomarkers for recurrence and chemosensitivity. Tumors not expressing MSH3 show elevated microsatellite alterations at selected tetranucleotide repeats (EMAST). EMAST reportedly occurs in several tumors. In colorectal cancer (CRC), EMAST was reportedly correlated with 5-fluorouracil (5-FU) sensitivity. However, EMAST prevalence in PDAC and its significance as a prognostic biomarker are unknown. This study aimed to investigate EMAST prevalence in PDAC and the associations between EMAST and pathological factors, EMAST and prognosis, and EMAST and MSH3 expression via immunohistochemistry (IHC). We assessed 40 PDAC patients undergoing surgery. Genomic DNA was extracted from tumors and normal tissues. EMAST and microsatellite instability-high (MSI-H) were analyzed using five polymorphic tetranucleotide markers and five mononucleotide markers, respectively. Tumor sections were stained for MSH3, and staining intensity was evaluated via the Histoscore (H-score). Eighteen of 40 (45%) PDAC patients were EMAST-positive; however, none were MSI-H-positive. Clinicopathological characteristics including overall survival (OS) and recurrence-free survival (RFS) were not significantly different between EMAST-positive and EMAST-negative patients (P = 0.45, 0.98 respectively). IHC was performed to evaluate MSH3 protein expression levels for the PDAC tissue specimens. H-scores of EMAST-positive patients ranged from 0 to 300 (median, 40) and those of EMAST-negative patients ranged from 0 to 300 (median, 170). MSH3 protein was not significantly downregulated in EMAST-positive patients (P = 0.07). This study is a preliminary study and the number of cases investigated was small, and thus, study of a larger cohort will reveal the clinical implication of EMAST.

A new method for discovering EMAST sequences in animal models of cancer

Elevated Microsatellite Alterations at Selected Tetranucleotide repeats (EMAST) occur in up to 60% of colorectal cancers and may associate with aggressive and advanced disease in patients. Although EMAST occurs in many cancer types, current understanding is limited due to the lack of an animal model. Reported here is the design and implementation of an algorithm for detecting EMAST repeats in mice. This algorithm incorporates properties of known human EMAST sequences to identify repeat sequences in animal genomes and was able to identify EMAST-like sequences in the mouse. Seven of the identified repeats were analyzed further in a colon cancer mouse model and six of the seven displayed EMAST instability characteristic of that seen in human colorectal cancers. In conclusion, the algorithm developed successfully identified EMAST repeats in an animal genome and, for the first time, EMAST has been shown to occur in a mouse model of colon cancer.

Deciphering Elevated Microsatellite Alterations at Selected Tetra/Pentanucleotide Repeats, Microsatellite Instability, and Loss of Heterozygosity in Colorectal Cancers

Elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) are common in colorectal cancers (CRCs). The association between EMAST and classic mono/dinucleotide microsatellite instability (MSI) is unknown. We assessed the stability of 13 tetranucleotide and three pentanucleotide repeat markers in tumor and normal tissue from 22 MSI-high and 107 microsatellite-stable CRC samples. When present, instability was observed at tetra/pentanucleotide repeats and was defined as elevated microsatellite alterations at selected tetra/pentanucleotide repeats-high (EMASTP-H; ≥30% instability), -low (EMASTP-L; <30% instability), or -stable (EMASTP-S). EMASTP instability, including high and low, was observed in 50 of 123 CRCs (41%), including all MSI-high tumors and 28 of 101 microsatellite-stable tumors (28%). MSI-high CRCs were more likely to be EMASTP-H compared with microsatellite-stable tumors with EMASTP instability. Tetranucleotide markers VWA and D13S317 were the two most frequently altered loci. Loss of heterozygosity was more common in EMASTP-L/S than in EMASTP-H CRCs. Frequencies of loss of heterozygosity at three loci were different between EMASTP-L and EMASTP-S tumors. In addition, right-sided tumor site, large tumor size, high tumor grade, and the presence of Crohn-like reaction were significantly associated with EMASTP-H CRCs. However, there were no differences in clinicopathologic features between EMASTP-L and EMASTP-S tumors. In summary, more CRCs exhibited genomic instability as EMASTP than as MSI. EMASTP instability may prove to be an important prognostic/therapeutic indicator in CRCs.

EMAST is associated with a poor prognosis in microsatellite instable metastatic colorectal cancer

Purpose

To determine the frequency and prognostic value of elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) in metastatic colorectal cancer (mCRC) patients in relation to microsatellite instability (MSI) status and MSH3 protein expression.

Material and Methods

The frequency of EMAST was evaluated in mCRC patients with MSI tumors and microsatellite stable (MSS) tumors. A literature overview was performed to compare the frequency of EMAST in our study with existing data. Immunohistochemistry for MSH3 was compared with EMAST status. Outcome was studied in terms of overall survival (OS) of mCRC patients with MSI and MSS tumors.

Results

EMAST was evaluated in 89 patients with MSI tumors (including 39 patients with Lynch syndrome) and 94 patients with MSS tumors. EMAST was observed in 45.9% (84 out of 183) of patients, with an increased frequency in MSI tumors (79.8% versus 13.8%, p < 0.001). We found no correlation between EMAST and MSH3 protein expression. There was no effect of EMAST on prognosis in patients with MSS tumors, but patients with MSI / non-EMAST tumors had a significantly better prognosis than patients with MSI / EMAST tumors (OS: HR 3.22, 95% CI 1.25-8.30).

Conclusion

Frequency of EMAST was increased in mCRC patients with MSI tumors, compared to MSS tumors. Our data suggest that the presence of EMAST correlates with worse OS in these patients. There was no effect of EMAST on the prognosis of patients with MSS tumors. A limitation of our study is the small number of patients in our subgroup analysis.

Prevalence and implications of elevated microsatellite alterations at selected tetranucleotides in cancer

Elevated microsatellite alterations at selected tetranucleotides (EMAST), a variation of microsatellite instability (MSI), has been reported in a variety of malignancies (e.g., neoplasias of the lung, head and neck, colorectal region, skin, urinary tract and reproductive organs). EMAST is more prominent at organ sites with potential external exposure to carcinogens (e.g., head, neck, lung, urinary bladder and colon), although the specific molecular mechanisms leading to EMAST remain elusive. Because it is often associated with advanced stages of malignancy, EMAST may be a consequence of rapid cell proliferation and increased mutagenesis. Moreover, defects in DNA mismatch repair enzyme complexes, TP53 mutation status and peritumoural inflammation involving T cells have been described in EMAST tumours. At various tumour sites, EMAST and high-frequency MSI share no clinicopathological features or molecular mechanisms, suggesting their existence as separate entities. Thus EMAST should be explored, because its presence in human cells may reflect both increased risk and the potential for early detection. In particular, the potential use of EMAST in prognosis and prediction may yield novel types of therapeutic intervention, particularly those involving the immune system. This review will summarise the current information concerning EMAST in cancer to highlight the knowledge gaps that require further research.

Epigenetic silencing of HOPX promotes cancer progression in colorectal cancer

Homeodomain-only protein X (HOPX)-β promoter methylation was recently shown to be frequent in human cancers and was suggested as tumor suppressor gene in esophageal and gastric cancer. The aim of this study was to investigate the mechanistic roles of HOPX-β promoter methylation and its clinical relevance in colorectal cancer (CRC). HOPX-β promoter methylation was assessed in human CRC cell lines and 294 CRC tissues. HOPX mRNA and protein levels were measured in relation to HOPX-β promoter methylation. The effects of forced HOPX expression on tumorigenesis were studied using in vitro and in vivo assays. The association between HOPX-β promoter methylation and clinical relevance of CRC patients was determined. HOPX-β promoter methylation is cancer-specific and frequently found in CRC cell lines and tissues, resulting in the down-regulation of HOPX mRNA and protein levels. In CRC cell lines, forced expression of HOPX suppressed proliferation, invasion, and anchorage-independent growth. DNA microarray analyses suggested critical downstream genes that are associated with cancer cell proliferation, invasion or angiogenesis. In a mouse xenograft model, HOPX inhibited tumorigenesis and angiogenesis. Finally, HOPX-β promoter methylation was associated with worse prognosis of stage III CRC patients (hazard ratio= 1.40, P = .035) and also with poor differentiation (P = .014). In conclusion, HOPX-β promoter methylation is a frequent and cancer-specific event in CRC progression. This epigenetic alteration may have clinical ramifications in the diagnosis and treatment of CRC patients.

MSH3-deficiency initiates EMAST without oncogenic transformation of human colon epithelial cells

BACKGROUND/AIM

Elevated microsatellite instability at selected tetranucleotide repeats (EMAST) is a genetic signature in certain cases of sporadic colorectal cancer and has been linked to MSH3-deficiency. It is currently controversial whether EMAST is associated with oncogenic properties in humans, specifically as cancer development in Msh3-deficient mice is not enhanced. However, a mutator phenotype is different between species as the genetic positions of repetitive sequences are not conserved. Here we studied the molecular effects of human MSH3-deficiency.

METHODS

HCT116 and HCT116+chr3 (both MSH3-deficient) and primary human colon epithelial cells (HCEC, MSH3-wildtype) were stably transfected with an EGFP-based reporter plasmid for the detection of frameshift mutations within an [AAAG]17 repeat. MSH3 was silenced by shRNA and changes in protein expression were analyzed by shotgun proteomics. Colony forming assay was used to determine oncogenic transformation and double strand breaks (DSBs) were assessed by Comet assay.

RESULTS

Despite differential MLH1 expression, both HCT116 and HCT116+chr3 cells displayed comparable high mutation rates (about 4×10(-4)) at [AAAG]17 repeats. Silencing of MSH3 in HCECs leads to a remarkable increased frameshift mutations in [AAAG]17 repeats whereas [CA]13 repeats were less affected. Upon MSH3-silencing, significant changes in the expression of 202 proteins were detected. Pathway analysis revealed overexpression of proteins involved in double strand break repair (MRE11 and RAD50), apoptosis, L1 recycling, and repression of proteins involved in metabolism, tRNA aminoacylation, and gene expression. MSH3-silencing did not induce oncogenic transformation and DSBs increased 2-fold.

CONCLUSIONS

MSH3-deficiency in human colon epithelial cells results in EMAST, formation of DSBs and significant changes of the proteome but lacks oncogenic transformation. Thus, MSH3-deficiency alone is unlikely to drive human colon carcinogenesis.

Microsatellite alterations at selected tetranucleotide repeats are associated with morphologies of colorectal neoplasias

BACKGROUND & AIMS

Elevated microsatellite alterations at selected tetranucleotide repeats (EMAST) occurs during microsatellite instability (MSI) that is not associated with major defects in DNA mismatch repair (MMR) but rather the reduced (heterogenous) expression of the MMR protein hMSH3; it occurs in sporadic colorectal tumors. We examined the timing of development of EMAST during progression of colorectal neoplasias and looked for correlations between EMAST and clinical and pathology features of tumors.

METHODS

We evaluated tumor samples from a cohort of patients that had 24 adenomas and 84 colorectal cancers. EMAST were analyzed after DNA microdissection of matched normal and tumor samples using the polymorphic tetranucleotide microsatellite markers MYCL1, D9S242, D20S85, D8S321, and D20S82; data were compared with clinical and pathology findings. Traditional MSI analysis was performed and hMSH3 expression was measured.

RESULTS

Moderately differentiated adenocarcinomas and poorly differentiated adenocarcinomas had higher frequencies of EMAST (56.9% and 40.0%, respectively) than well-differentiated adenocarcinomas (12.5%) or adenomas (33.3%) (P = .040). In endoscopic analysis, ulcerated tumors had a higher frequency of EMAST (52.3%) than flat (44.0%) or protruded tumors (20.0%) (P = .049). In quantification, all tumors with >3 tetranucleotide defects lost MSH3 (>75% of cells); nuclear heterogeneity of hMSH3 occurred more frequently in EMAST-positive (40.0%) than in EMAST-negative tumors (13.2%) (P = .010).

CONCLUSIONS

EMAST is acquired during progression of adenoma and well-differentiated carcinomas to moderately and poorly differentiated carcinomas; it correlates with nuclear heterogeneity for hMSH3. Loss of hMSH3 corresponds with multiple tetranucleotide frameshifts. The association between EMAST and ulcerated tumors might result from increased inflammation.

Relationship of EMAST and microsatellite instability among patients with rectal cancer

BACKGROUND

Elevated microsatellite instability at selected tetranucleotide repeats (EMAST) is a genetic signature identified in 60% of sporadic colon cancers and may be linked with heterogeneous expression of the DNA mismatch repair (MMR) protein hMSH3. Unlike microsatellite instability-high (MSI-H) in which hypermethylation of hMLH1 occurs followed by multiple susceptible gene mutations, EMAST may be associated with inflammation and subsequent relaxation of MMR function with the biological consequences not known. We evaluated the prevalence of EMAST and MSI in a population-based cohort of rectal cancers, as EMAST has not been previously determined in rectal cancers.

METHODS

We analyzed 147 sporadic cases of rectal cancer using five tetranucleotide microsatellite markers and National-Cancer-Institute-recommended MSI (mononucleotide and dinucleotide) markers. EMAST and MSI determinations were made on analysis of DNA sequences of the polymerase chain reaction products and determined positive if at least two loci were found to have frame-shifted repeats upon comparison between normal and cancer samples from the same patient. We correlated EMAST data with race, gender, and tumor stage and examined the samples for lymphocyte infiltration.

RESULTS

Among this cohort of patients with rectal cancer (mean age 62.2 ± 10.3 years, 36% female, 24% African American), 3/147 (2%) showed MSI (three males, two African American) and 49/147 (33%) demonstrated EMAST. Rectal tumors from African Americans were more likely to show EMAST than Caucasians (18/37, 49% vs. 27/104, 26%, p = 0.014) and were associated with advanced stage (18/29, 62% EMAST vs. 18/53, 37%, non-EMAST p = 0.02). There was no association between EMAST and gender. EMAST was more prevalent in rectal tumors that showed peri-tumoral infiltration compared to those without (30/49, 60% EMAST vs. 24/98, 25% non-EMAST, p = 0.0001).

CONCLUSIONS

EMAST in rectal cancer is common and MSI is rare. EMAST is associated with African-American race and may be more commonly seen with metastatic disease. The etiology and consequences of EMAST are under investigation, but its association with immune cell infiltration suggests that inflammation may play a role for its development.