Clinical and molecular characterisation of hereditary and sporadic metastatic colorectal cancers harbouring microsatellite instability/DNA mismatch repair deficiency

Mismatch Repair (MMR) Gene Mutation Carriers Have Favorable Outcome in Colorectal and Endometrial Cancer: A Prospective Cohort Study

Germline (Lynch syndrome, LS) and somatic deficiencies of mismatch repair proteins (MMRd) are linked to colorectal and endometrial cancer; however, their prognostic impact in Asian populations remains unclear. This prospective cohort study aimed to determine the prevalence and outcome of germline and somatic MMRd in cancer patients suspected of LS. Patients with colorectal or endometrial cancer suspected of LS were enrolled and underwent gene sequencing for germline MMRd (gMMRd) and immunohistochemistry staining of MMR proteins in a subset of the pathological samples (pMMRd). Among the 451 enrolled patients, 36 patients were gMMRd (+). Compared with gMMRd (-) patients, the 10-year relapse-free survival in gMMRd (+) patients was significantly higher (100% vs. 77.9%; p = 0.006), whereas the 10-year overall survival was similar (100% vs. 90.9%; p = 0.12). Among the 102 gMMRd (-) patients with available pMMR status, 13.7% were pMMRd (+). The 5-year relapse-free survival was 62.9% in gMMRd (-) pMMRd (+) patients and 35.0% in gMMRd (-) pMMRd (-) patients, both lower than gMMRd (+) patients (100%; p < 0.001). This study showed that having LS confers a favorable outcome in colorectal and endometrial cancer patients and highlights the importance of germline genetic testing following the detection of somatic MMRd.

Relationship Between ABO Blood Group and Microsatellite Instability in Colorectal Cancer: A Retrospective Single-Center Study

PURPOSE

Colorectal cancer (CRC) is the second most common cancer in both women and men. Microsatellite instability-high (MSI-H) CRC is a molecular subgroup and has distinct clinical and pathologic features from microsatellite stable (MSS) CRC. Studies have suggested an association between hereditary antigens in ABO blood group system and the risk of developing various cancers but the relationship between blood groups and MSI-H CRC has not been investigated. This study aimed to investigate this relationship and its possible effect on clinicopathological features in patients with CRC.

METHODS

This is a retrospective cross-sectional single-center study including pathology-confirmed CRC patients. Demographic and clinicopathological features, blood groups, and microsatellite status were examined among two groups. Microsatellite instability was examined by immunohistochemistry (IHC) in pathology specimen.

RESULTS

A total of 144 patients, 72 patients with MSI-H CRC and 72 patients with MSS CRC, were included in the study. Among all patients, median age was 61.7 ± 12.9 (range 27-89) and 57.6% were male. MSI-H and MSS groups were similar in terms of age, gender distribution, and comorbidities. Patients with MSI-H CRC had significantly common O-blood group than control group (44.4% vs 18.1%, p: 0.001). In multivariate analysis, O-blood group was 4.2 times more common in the MSI-H patient group (95% CI: 1.514-11.819, p: 0.006). Also patients with MSI-H CRC were found to have significantly more right-sided, high-grade tumors and early-stage disease.

CONCLUSIONS

MSI-H CRC is an important subgroup in colon cancer with different molecular and clinicopathological features. It was observed that O-blood group was 4.2 times more common in MSI-H CRC. We believe that clarifying the relationship between microsatellite instability and O-blood group and its possible genetic and epigenetic mechanisms in larger studies will enable us to better understand tumor behavior and prognosis, also affect our treatment choices of these patient groups.

Molecular profile of gastric adenocarcinoma, relevant epidemiological factors - Systematic review and meta-analysis relating sex with Epstein-Barr virus and unstable microsatellites subtypes

INTRODUCTION

Gastric epithelial tumors exhibit morphological heterogeneity, diverse biological behaviors, and different oncopathological pathways. The Cancer Genome Atlas (TCGA) proposed a molecular classification of gastric adenocarcinomas based on genetic and molecular findings, which shows particular characteristics of diagnosis, prognosis, and indirectly, therapeutic alternatives. Within this classification, Epstein-Barr virus-positive (EBV+) and high microsatellite instability (MSI-H) subtypes stand out as subtypes that present a less aggressive biological behavior and a highly mutilated phenotype. This study conducted a systematic review with an emphasis on epidemiological and prognostic factors based on the molecular classification proposed by TCGA.

METHODS

A broad, comprehensive, and reproducible search with methodological rigor was conducted for study selection using the ROBINS-I and GRADEpro protocols and appropriate combinations of keywords.

RESULTS

A total of 25 studies were selected: six with a complete classification similar to TCGA and 19 with a distinction between MSI-H and EBV+. The application of meta-analysis calculations reinforces the prevalence of positive Epstein-Barr adenocarcinomas in males and high microsatellite instability in females, with a high level of certainty of evidence and low risk of bias in the analyzed studies due to the rigorous methods used.

CONCLUSION

The molecular classification proposed by TCGA shows limited dissemination, with MSI-H and EBV+ subtypes being the most researched, probably due to the benefit of the association with immunotherapies. However, the subclassification cannot be restricted to less than a quarter of the cases, and improvements in this aspect are urgent for the construction of knowledge on this important topic of global health.

Comprehensive genomic characterization of sporadic synchronous colorectal cancer: Implications for treatment optimization and clinical outcome

Sporadic synchronous colorectal cancer (SCRC) refers to multiple primary CRC tumors detected simultaneously in an individual without predisposing hereditary conditions, which accounts for the majority of multiple CRCs while lacking a profound understanding of the genomic landscape and evolutionary dynamics to optimize its treatment. In this study, 103 primary tumor samples from 51 patients with SCRC undergo whole-exome sequencing. The germline and somatic mutations and evolutionary and clinical features are comprehensively investigated. Somatic genetic events are largely inconsistent between paired tumors. Compared with solitary CRC, SCRCs have higher prevalence of tumor mutation burden high (TMB-H; 33.3%) and microsatellite-instability high (MSI-H; 29.4%) and different mutation frequencies in oncogenic signaling pathways. Moreover, neutrally evolving SCRC tumors are associated with higher intratumoral heterogeneity and better prognosis. These findings unveil special molecular features, carcinogenesis, and prognosis of sporadic SCRC. Strategies for targeted therapy and immunotherapy should be optimized accordingly.

Complete pathological response after chemotherapy or immune checkpoint inhibitors in deficient MMR metastatic colorectal cancer: Results of a retrospective multicenter study

About 5% of the patients with metastatic colorectal cancers (mCRC) present microsatellite instability (MSI)/deficient mismatch repair system (dMMR). While metastasectomy is known to improve overall and progression-free survival in mCRC, specific results in selected patients with dMMR/MSI mCRC are lacking. Our study aimed to describe metastasectomy results, characterize histological response and evaluate pathological complete response (pCR) rate in patients with dMMR/MSI mCRC. We retrospectively reviewed data from all consecutive patients with dMMR/MSI mCRC who underwent surgical metastasectomy between January 2010 and June 2021 in 17 French centers. Primary outcome was to assess the pCR rate defined by tumor regression grade (TRG) 0. Secondary endpoints included relapse-free survival (RFS) and overall survival (OS), and explored TRG as predictive factor for RFS and OS. Among the 88 patients operated, 109 metastasectomies were performed in 81 patients after neoadjuvant treatment [chemotherapy ± targeted therapy (CTT): 69, 85.2%; immunotherapy (ICI): 12, 14.8%], and pCR was achieved in 13 (16.1%) patients. Among the latter, pCR rate were 10.2% in the patients having received CTT (N = 7) and 50.0% in the patients treated with ICI (N = 6). Radiological response did not predict TRG. With a median follow-up of 57.9 (IQR 34.2-81.6) months, median RFS was 20.2 (15.4-not reached) months, median OS was not reached. Major pathological responses (TRG0 + TRG1) were significantly associated with longer RFS (HR 0.12, 95% CI 0.03-0.55; P = .006). The pCR rate of 16.1% achieved with neoadjuvant treatment in patients with dMMR/MSI mCRC is consistent with previously reported rates in pMMR/MSS mCRC. Immunotherapy showed better pCR rate than chemotherapy ± targeted therapy. Further prospective trials are needed to validate immunotherapy as neoadjuvant treatment in resectable/potentially resectable dMMR/MSI mCRC and identify predictive factors for pCR.

BRAF V600E/RAS Mutations and Lynch Syndrome in Patients With MSI-H/dMMR Metastatic Colorectal Cancer Treated With Immune Checkpoint Inhibitors

BACKGROUND

We pooled data from 2 cohorts of immune checkpoint inhibitors-treated microsatellite instability-high/mismatch repair-deficient (MSI/dMMR) metastatic colorectal cancer patients to evaluate the prognostic value of RAS/BRAFV600E mutations and Lynch syndrome (LS).

PATIENTS AND METHODS

Patients were defined as LS-linked if germline mutation was detected and as sporadic if loss of MLH1/PMS2 expression with BRAFV600E mutation and/or MLH1 promoter hypermethylation, or biallelic somatic MMR genes mutations were found. Progression-free survival (PFS) and overall survival (OS) were adjusted on prognostic modifiers selected on unadjusted analysis (P < .2) if limited number of events.

RESULTS

Of 466 included patients, 305 (65.4%) and 161 (34.5%) received, respectively, anti-PD1 alone and anti-PD1+anti-CTLA4 in the total population, 111 (24.0%) were treated in first-line; 129 (28.8%) were BRAFV600E-mutated and 153 (32.8%) RAS-mutated. Median follow-up was 20.9 months. In adjusted analysis of the whole population (PFS/OS events = 186/133), no associations with PFS and OS were observed for BRAFV600E-mutated (PFS HR= 1.20, P = .372; OS HR = 1.06, P = .811) and RAS-mutated patients (PFS HR = 0.93, P = .712, OS HR = 0.75, P = .202). In adjusted analysis in the Lynch/sporadic status-assigned population (n = 242; PFS/OS events = 80/54), LS-liked patients had an improved PFS compared to sporadic cases (HR = 0.49, P = .036). The adjusted HR for OS was 0.56 with no significance (P = .143). No adjustment on BRAFV600E mutation was done due to collinearity.

CONCLUSION

In this cohort, RAS/BRAFV600E mutations were not associated with survival while LS conferred an improved PFS.

Immunotherapy for Colorectal Cancer with High Microsatellite Instability: The Ongoing Search for Biomarkers

Microsatellite instability (MSI) is a biological condition associated with inflamed tumors, high tumor mutational burden (TMB), and responses to immune checkpoint inhibitors. In colorectal cancer (CRC), MSI tumors are found in 5% of patients in the metastatic setting and 15% in early-stage disease. Following the impressive clinical activity of immune checkpoint inhibitors in the metastatic setting, associated with deep and long-lasting responses, the development of immune checkpoint inhibitors has expanded to early-stage disease. Several phase II trials have demonstrated a high rate of pathological complete responses, with some patients even spared from surgery. However, in both settings, not all patients respond and some responses are short, emphasizing the importance of the ongoing search for accurate biomarkers. While various biomarkers of response have been evaluated in the context of MSI CRC, including B2M and JAK1/2 mutations, TMB, WNT pathway mutations, and Lynch syndrome, with mixed results, liver metastases have been associated with a lack of activity in such strategies. To improve patient selection and treatment outcomes, further research is required to identify additional biomarkers and refine existing ones. This will allow for the development of personalized treatment approaches and the integration of novel therapeutic strategies for MSI CRC patients with liver metastases.

Prognostic value of Lynch syndrome, BRAFV600E , and RAS mutational status in dMMR/MSI-H metastatic colorectal cancer in a pooled analysis of Dutch and French cohorts

BACKGROUND

Current knowledge on prognostic biomarkers (especially BRAFV600E /RAS mutations) in metastatic colorectal cancer (mCRC) is mainly based on mCRC patients with proficient mismatch repair (pMMR) tumors. It is uncertain whether these biomarkers have the same prognostic value in mCRC patients with deficient mismatch repair (dMMR) tumors.

METHODS

This observational cohort study combined a population-based Dutch cohort (2014-2019) and a large French multicenter cohort (2007-2017). All mCRC patients with a histologically proven dMMR tumor were included.

RESULTS

In our real-world data cohort of 707 dMMR mCRC patients, 438 patients were treated with first-line palliative systemic chemotherapy. Mean age of first-line treated patients was 61.9 years, 49% were male, and 40% had Lynch syndrome. BRAFV600E mutation was present in 47% of tumors and 30% harbored a RAS mutation. Multivariable regression analysis on OS showed significant hazard rates (HR) for known prognostic factors as age and performance status, however showed no significance for Lynch syndrome (HR: 1.07, 95% CI: 0.66-1.72), BRAFV600E mutational status (HR: 1.02, 95% CI: 0.67-1.54), and RAS mutational status (HR: 1.01, 95% CI: 0.64-1.59), with similar results for PFS.

CONCLUSION

BRAFV600E and RAS mutational status are not associated with prognosis in dMMR mCRC patients, in contrast to pMMR mCRC patients. Lynch syndrome is also not an independent prognostic factor for survival. These findings underline that prognostic factors of patients with dMMR mCRC are different of those with pMMR, which could be taken into consideration when prognosis is used for clinical decision-making in dMMR mCRC patients and underline the complex heterogeneity of mCRC.

DNA Damage Repair Pathways in Prostate Cancer: A Narrative Review of Molecular Mechanisms, Emerging Biomarkers and Therapeutic Targets in Precision Oncology

Prostate cancer (PCa) has a distinct molecular signature, including characteristic chromosomal translocations, gene deletions and defective DNA damage repair mechanisms. One crucial pathway involved is homologous recombination deficiency (HRD) and it is found in almost 20% of metastatic castrate-resistant PCa (mCRPC). Inherited/germline mutations are associated with a hereditary predisposition to early PCa development and aggressive behavior. BRCA2, ATM and CHECK2 are the most frequently HRD-mutated genes. BRCA2-mutated tumors have unfavorable clinical and pathological characteristics, such as intraductal carcinoma. PARP inhibitors, due to the induction of synthetic lethality, have been therapeutically approved for mCRPC with HRD alterations. Mutations are detected in metastatic tissue, while a liquid biopsy is utilized during follow-up, recognizing acquired resistance mechanisms. The mismatch repair (MMR) pathway is another DNA repair mechanism implicated in carcinogenesis, although only 5% of metastatic PCa is affected. It is associated with aggressive disease. PD-1 inhibitors have been used in MMR-deficient tumors; thus, the MMR status should be tested in all metastatic PCa cases. A surrogate marker of defective DNA repair mechanisms is the tumor mutational burden. PDL-1 expression and intratumoral lymphocytes have ambivalent predictive value. Few experimental molecules have been so far proposed as potential biomarkers. Future research may further elucidate the role of DNA damage pathways in PCa, revealing new therapeutic targets and predictive biomarkers.

Efficacy of immunotherapy in mismatch repair-deficient advanced colorectal cancer in routine clinical practice. An AGEO study

BACKGROUND

Immunotherapy demonstrated remarkable efficacy in metastatic colorectal cancers (mCRCs) with mismatch repair deficiency (MMRd)/microsatellite instability (MSI). However, data regarding efficacy and safety of immunotherapy in the routine clinical practice are scarce.

PATIENTS AND METHODS

This is a retrospective, multicenter study aiming to evaluate efficacy and safety of immunotherapy in routine clinical practice and to identify predictive markers for long-term benefit. Long-term benefit was defined as progression-free survival (PFS) exceeding 24 months. All patients who received immunotherapy for an MMRd/MSI mCRC were included. Patients who received immunotherapy in combination with another known effective therapeutic class agent (chemotherapy or tailored therapy) were excluded.

RESULTS

Overall, 284 patients across 19 tertiary cancer centers were included. After a median follow-up of 26.8 months, the median overall survival (mOS) was 65.4 months [95% confidence interval (CI) 53.8 months-not reached (NR)] and the median PFS (mPFS) was 37.9 months (95% CI 30.9 months-NR). There was no difference in terms of efficacy or toxicity between patients treated in the real-world or as part of a clinical trial. Overall, 46.6% of patients had long-term benefit. Independent markers associated with long-term benefit were Eastern Cooperative Oncology Group-performance status (ECOG-PS) 0 (P = 0.025) and absence of peritoneal metastases (P = 0.009).

CONCLUSIONS

Our study confirms the efficacy and safety of immunotherapy in patients with advanced MMRd/MSI CRC in the routine clinical practice. ECOG-PS score and absence of peritoneal metastases provide simple markers that could help identify patients who benefit the most from this treatment.

Development and Interpretation of a Clinicopathological-Based Model for the Identification of Microsatellite Instability in Colorectal Cancer

Chemotherapy is not recommended for patients with deficient mismatch repair (dMMR) in colorectal cancer (CRC); therefore, assessing the status of MMR is crucial for the selection of subsequent treatment. This study is aimed at building predictive models to accurately and rapidly identify dMMR. A retrospective analysis was performed at Wuhan Union Hospital between May 2017 and December 2019 based on the clinicopathological data of patients with CRC. The variables were subjected to collinearity, least absolute shrinkage and selection operator (LASSO) regression, and random forest (RF) feature screening analyses. Four sets of machine learning models (extreme gradient boosting (XGBoost), support vector machine (SVM), naive Bayes (NB), and RF) and a conventional logistic regression (LR) model were built for model training and testing. Receiver operating characteristic (ROC) curves were plotted to evaluate the predictive performance of the developed models. In total, 2279 patients were included in the study and were randomly divided into either the training or test group. Twelve clinicopathological features were incorporated into the development of the predictive models. The area under curve (AUC) values of the five predictive models were 0.8055 for XGBoost, 0.8174 for SVM, 0.7424 for NB, 8584 for RF, and 0.7835 for LR (Delong test, P value < 0.05). The results showed that the RF model exhibited the best recognition ability and outperformed the conventional LR method in identifying dMMR and proficient MMR (pMMR). Our predictive models based on routine clinicopathological data can significantly improve the diagnostic performance of dMMR and pMMR. The four machine learning models outperformed the conventional LR model.

Association Between Survival and Metastatic Site in Mismatch Repair-Deficient Metastatic Colorectal Cancer Treated With First-line Pembrolizumab

Importance

Metastatic colorectal cancer (mCRC) with deficient DNA mismatch repair (dMMR) shows frequent and durable responses to programmed cell death 1 blockade. While most of these tumors are sporadic and observed in older patients, first-line pembrolizumab data are limited to findings from the KEYNOTE-177 trial (A Phase III Study of Pembrolizumab [MK-3475] vs Chemotherapy in Microsatellite Instability-High [MSI-H] or Mismatch Repair Deficient [dMMR] Stage IV Colorectal Carcinoma).

Objective

To investigate outcome with first-line pembrolizumab monotherapy in mostly older patients with dMMR mCRC at a multisite clinical practice.

Design, Setting, and Participants

This cohort study included consecutive patients with dMMR mCRC who received pembrolizumab monotherapy between April 1, 2015, and January 1, 2022, at Mayo Clinic sites and the Mayo Clinic Health System. Patients were identified from review of electronic health records at the sites, which included the evaluation of digitized radiologic imaging studies.

Intervention

Patients with dMMR mCRC received first-line pembrolizumab, 200 mg, every 3 weeks.

Main Outcomes and Measures

The primary study end point was progression-free survival (PFS), which was analyzed using the Kaplan-Meier method and a multivariable stepwise Cox proportional hazards regression model. Clinicopathological features, including metastatic site and molecular data (BRAF V600E and KRAS), were also analyzed along with tumor response rate, which was determined using Response Evaluation Criteria in Solid Tumors, version 1.1.

Results

The study cohort included 41 patients (median [IQR] age at treatment initiation, 81 [76-86] years; 29 females [71%]) with dMMR mCRC. Of these patients, 30 (79%) had the BRAF V600E variant and 32 (80%) were classified as having sporadic tumors. Median (range) follow-up was 23 (3-89) months. Median (IQR) number of treatment cycles was 9 (4-20). Overall response rate was 49% (20 of 41 patients), including 13 patients (32%) with complete responses and 7 (17%) with partial responses. Median (IQR) PFS was 21 (95% CI, 6-39) months. Liver as a site of metastasis was associated with significantly poorer PFS vs nonliver metastasis (adjusted hazard ratio, 3.40; 95% CI, 1.27-9.13; adjusted P = .01). Complete and partial responses were observed in 3 patients (21%) with liver metastasis vs 17 patients (63%) with nonliver metastases. Treatment-related grade 3 or 4 adverse events were observed in 8 patients (20%), 2 of whom discontinued therapy; there was 1 treatment-related death.

Conclusions and Relevance

This cohort study found a clinically significant prolongation of survival in older patients with dMMR mCRC who were treated with first-line pembrolizumab in routine clinical practice. Furthermore, liver vs nonliver metastasis was associated with poorer survival in this patient population, which suggests that the metastatic site has implications for survival outcome.

Clinicopathological characteristics of high microsatellite instability/mismatch repair-deficient colorectal cancer: A narrative review

Colorectal cancers (CRCs) with high microsatellite instability (MSI-H) and deficient mismatch repair (dMMR) show molecular and clinicopathological characteristics that differ from those of proficient mismatch repair/microsatellite stable CRCs. Despite the importance of MSI-H/dMMR status in clinical decision making, the testing rates for MSI and MMR in clinical practice remain low, even in high-risk populations. Additionally, the real-world prevalence of MSI-H/dMMR CRC may be lower than that reported in the literature. Insufficient MSI and MMR testing fails to identify patients with MSI-H/dMMR CRC, who could benefit from immunotherapy. In this article, we describe the current knowledge of the clinicopathological features, molecular landscape, and radiomic characteristics of MSI-H/dMMR CRCs. A better understanding of the importance of MMR/MSI status in the clinical characteristics and prognosis of CRC may help increase the rates of MMR/MSI testing and guide the development of more effective therapies based on the unique features of these tumors.

Prognostic significance and immune landscape of a fatty acid metabolism-related gene signature in colon adenocarcinoma

Background: Fatty acid metabolism (FAM), as a hallmark of caner, plays important roles in tumor initiation and carcinogenesis. However, the significance of fatty acid metabolism-related genes in colon adenocarcinoma (COAD) are largely unknown. Methods: RNA sequencing data and clinical information were downloaded from the Cancer Genome Atlas (TCGA) cohort. Univariate and multivariate Cox regression analyses were utilized to construct a fatty acid metabolism-related gene signature. Kaplan-Meier survival and receiver operating characteristic (ROC) analyses were used to verify the performance of this signature. GEO datasets were applied to validate the signature. Maftools package was utilized to analyze the mutation profiles of this signature. Correlation between the risk signature and stemness scores was compared by RNA stemness score (RNAss). Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genomes (KEGG) and gene set variation analysis (GSVA) were performed to explore the potential functions and signaling pathways. Immune landscape of the signature was explored by analyzing different immune cells infiltration, immune functions and microsatellite instability. A nomogram was constructed by combining the risk signature and multiple clinical factors. Expression levels and prognostic values of the risk genes were revealed in the cancer genome atlas and GEO databases. Moreover, the expression the risk genes were measured in cell lines using real time quantitative PCR (qRT-PCR). Results: Eight fatty acid metabolism-related genes (CD36, ENO3, MORC2, PTGR1, SUCLG2, ELOVL3, ELOVL6 and CPT2) were used to construct a risk signature. This signature demonstrated better prognostic value than other clinicopathological parameters, with AUC value was 0.734 according to the cancer genome atlas database. There was negative correlation between the riskscore and RNA stemness score. The patients in the high-risk group demonstrated higher infiltration of M0 macrophages, and less infiltration of activated CD4 memory T cells and Eosinophils. There were more MSI patients in the high-risk group than those in the low-risk group (38% vs. 30%). The risk scores of patients in the MSI group were slightly higher than those in the microsatellite stability group. Gene ontology, kyoto encyclopedia of genes and genomes and gene set variation analysis enrichment analyses showed that several metabolism-related functions and signaling pathways were enriched. A nomogram showed good predictive capability of the signature. Moreover, qRT-PCR revealed upregulated expression of ENO3, MORC2, SUCLG2 and ELOVL6, and downregulated expression of CPT2 in all examined colon adenocarcinoma cell lines. Conclusion: This study provided novel insights into a fatty acid metabolism-related signature in the prognosis an immune landscape of colon adenocarcinoma patients.

Clinicopathological and molecular characterization of deficient mismatch repair colorectal cancer

Tumors demonstrating deficient mismatch repair (dMMR) account for 12%-15% of colorectal cancers (CRCs), but their characteristics have not been fully elucidated. The aim of this study was to characterize dMMR CRCs in terms of clinicopathological findings and molecular alterations. Immunostaining for mismatch repair (MMR) proteins was performed to determine MMR status, and then MLH1 promoter methylation and genetic variants of 25 genes involved in colorectal carcinogenesis were analyzed by next-generation sequencing in dMMR tumors. Coexistence of precancerous lesions was histologically evaluated to characterize the type of precursors. Immunohistochemistry revealed 34 dMMR tumors in 492 CRCs. Among dMMR CRCs, there were 25 MLH1 methylation-positive, 16 BRAF V600E variant-positive, and 7 KRAS variant-positive tumors. Positive MLH1 methylation was associated with BRAF V600E, older age, and right-side tumor location. MLH1 methylated BRAF/KRAS wild-type tumors were distinct in that all 5 tumors possessed variants in ligand-independent WNT signaling genes including APC, AXIN2, and CTNNB1. Among 10 dMMR CRCs that presented with precancerous lesions, 4 BRAF variant-positive, 1 KRAS variant-positive, and 2 BRAF/KRAS wild-type MLH1 methylated tumors coexisted with serrated lesions, whereas 1 MLH1 methylated BRAF/KRAS wild-type tumor and 2 MLH1 unmethylated tumors accompanied conventional adenomas. The present study characterized distinct subgroups of dMMR CRCs based on molecular alterations including MLH1 methylation and variants in BRAF, KRAS, and ligand-independent WNT signaling genes. The existence of distinct precursor lesions including serrated lesion and conventional adenoma further illustrates the involvement of heterogeneous carcinogenetic pathways in the development of dMMR CRCs.

The distinct clinical trajectory, metastatic sites, and immunobiology of microsatellite-instability-high cancers

Microsatellite-instability-high (MSI-H) cancers form a spectrum of solid organ tumors collectively known as Lynch Syndrome cancers, occurring not only in a subset of colorectal, endometrial, small bowel, gastric, pancreatic, and biliary tract cancers but also in prostate, breast, bladder, and thyroid cancers. Patients with Lynch Syndrome harbor germline mutations in mismatch repair genes, with a high degree of genomic instability, leading to somatic hypermutations and, therefore, oncogenesis and cancer progression. MSI-H cancers have unique clinicopathological characteristics compared to their microsatellite-stable (MSS) counterparts, marked by a higher neoantigen load, immune cell infiltration, and a marked clinical response to immune checkpoint blockade. Patients with known Lynch Syndrome may be detected early through surveillance, but some patients present with disseminated metastatic disease. The treatment landscape of MSI-H cancers, especially colorectal cancers, has undergone a paradigm shift and remains to be defined, with immune checkpoint blockade coming to the forefront of treatment strategies in the stage IV setting. We summarize in this review the clinical features of MSI-H cancers with a specific interest in the pattern of spread or recurrence, disease trajectory, and treatment strategies. We also summarize the tumor-immune landscape and genomic profile of MSI-H cancers and potential novel therapeutic strategies.

The Role of Biomarkers in the Management of Colorectal Liver Metastases

Simple Summary

Colorectal cancer remains one of the most significant sources of cancer-related morbidity and mortality worldwide. The liver is the most common site of metastatic spread. Multiple modalities exist to manage and potentially cure patients with metastatic colorectal cancer. However, reliable biomarkers to assist with clinical decision-making are limited. Recent advances in genomic sequencing technology have greatly expanded our knowledge of colorectal cancer carcinogenesis and significantly reduced the cost and timing of the investigation. In this article, we discuss the current utility of biomarkers in the management of colorectal cancer liver metastases.

Abstract

Surgical management combined with improved systemic therapies have extended 5-year overall survival beyond 50% among patients with colorectal liver metastases (CRLM). Furthermore, a multitude of liver-directed therapies has improved local disease control for patients with unresectable CRLM. Unfortunately, a significant portion of patients treated with curative-intent hepatectomy develops disease recurrence. Traditional markers fail to risk-stratify and prognosticate patients with CRLM appropriately. Over the last few decades, advances in molecular sequencing technology have greatly expanded our knowledge of the pathophysiology and tumor microenvironment characteristics of CRLM. These investigations have revealed biomarkers with the potential to better inform management decisions in patients with CRLM. Actionable biomarkers such as RAS and BRAF mutations, microsatellite instability/mismatch repair status, and tumor mutational burden have been incorporated into national and societal guidelines. Other biomarkers, including circulating tumor DNA and radiomic features, are under active investigation to evaluate their clinical utility. Given the plethora of therapeutic modalities and lack of evidence on timing and sequence, reliable biomarkers are needed to assist clinicians with the development of patient-tailored management plans. In this review, we discuss the current evidence regarding biomarkers for patients with CRLM.

The Evolving Landscape of Immunotherapy in Locally Advanced Rectal Cancer Patients

Simple Summary

At the last 2022 annual ASCO meeting, impressive results of anti-PD1 activity in clinical stage 2 and 3 microsatellite instable rectal cancer patients have been published. Moreover, a growing number of studies assessed the synergism between neoadjuvant (chemo)radiotherapy and immunotherapy in microsatellite stable localized rectal cancer patients. Major findings of immunotherapy activity and efficacy in localized rectal cancer, according to microsatellite status, are discussed in this commentary.

Abstract

Standard treatments of localized rectal cancer are surgery or the multimodal approach with neoadjuvant treatments (chemo-radiotherapy, short-course radiotherapy, induction, or consolidation chemotherapy) followed by surgery. In metastatic colorectal cancer (mCRC), immune checkpoint inhibitors (ICIs) are now the first choice in patients with a deficient mismatch repair system/microsatellite instability (dMMR/MSI-H) and are being explored in combination with chemotherapy to rewire the immune system against malignant cells in subjects with proficient mismatch repair system/microsatellite low (pMMR/MSI-L) cancers, with promising signals of efficacy. Recently, some efforts have been made to translate ICIs in earlier stages of CRC, including localized rectal cancer, with breakthrough efficacy and an organ preservation rate of mono-immunotherapy in dMMR/MSI-H patients and promising anti-tumor activity of immunotherapy plus neoadjuvant (chemo)radiotherapy in pMMR/MSI-L subjects. Here, we present the rationale, results, and limitations of the most remarkable trials assessing ICIs in dMMR/MSI-H and pMMR/MSI-L localized rectal cancer patients, at the same time highlighting the most promising research perspectives that have followed these studies.

Acellular mucin in lymph nodes isolated from treatment-naïve colorectal cancer resections: a clinicopathologic analysis of 16 cases

Lymph nodes with acellular mucin harvested from treated colorectal cancers (CRC) are staged as pN0. However, there is variability among pathologists while reporting the pN stage when acellular mucin is found within nodes of untreated CRCs. While the UICC guidelines suggest staging them as pN1, the AJCC and CAP do not offer any recommendations. In order to characterize their clinicopathologic features and outcome, we compared 16 untreated CRCs (study group; mean age: 68 years) harboring nodes with acellular mucin with 34 pN0 and 25 pN1 untreated CRC controls. All tumors were unifocal; 12 (75%) were right-sided lesions. Most cases (75%) showed one node with acellular mucin (range: 1-3). MMR-deficient tumors were significantly more common in the study group (83%) compared to pN0 (33%; p = 0.006) and pN1 controls (8%; p < 0.001). The overall survival of study group patients was closer to pN0 compared to pN1 controls; however, this difference was not statistically significant. In conclusion, untreated CRC that harbor acellular mucin within lymph nodes commonly present as right-sided, MMR-deficient tumors in older women that show a non-mucinous phenotype. While the limited number of cases precludes us from making any formal recommendations about staging, we suggest that the finding of acellular mucin in a node should prompt evaluation of deeper levels (with or without cytokeratin immunohistochemistry) and submission of all pericolonic fat for additional lymph node harvest. Whether acellular mucin in nodes of untreated CRCs is related to the indolent biology of the disease, a robust local immune response or MMR deficiency requires further investigation.

Microsatellite instability and chemosensitivity in solid tumours

The use of biomarkers that influence a targeted choice in cancer treatments is the future of medical oncology. Within this scenario, in recent years, an important role has been played by knowledge of microsatellite instability (MSI), a molecular fingerprint that identifies defects in the mismatch repair system. This knowledge has changed clinical practice in the adjuvant setting of colon cancer, and its role in the neoadjuvant setting in gastric tumours is becoming increasingly interesting, as well as in endometrial cancers in both early and advanced diseases. Furthermore, it has undoubtedly conditioned the first lines of treatment in the metastatic setting in different types of cancers. The incidence of MSI is different in different cancer types, as well as in early cancers versus metastatic disease. Knowing the incidence of MSI in the various histologies can provide insight into the potential use of this biomarker considering its prognostic value, especially in the early stages, and its predictive role with respect to treatment response. In particular, MSI can guide the choice of chemotherapy treatments in the adjuvant setting of colon and perioperative setting in gastric tumours, which could lead to immunotherapy treatments in these patients in both the early stages of the disease and the metastatic setting where the response to immunotherapy drugs in diseases with MSI is now well established. In this review, we focus on colon, gastric and endometrial cancers, and we briefly discuss other cancer types where MSI could have a potential role in oncological treatment decisions.

Microsatellite instability in colon cancer: A single center experience from North India

Background

Due to the defects of mismatch repair (MMR) genes MLH1, PMS2, MSH2, and MSH6, the mutations which occur in microsatellite region are not repaired during deoxyribonucleic acid synthesis, leading to microsatellite instability (MSI). MSI is one of the major molecular changes that occur in colorectal carcinoma (CRC). Studies have shown that MMR deficient CRC has different clinicopathological characteristics and a better stage adjusted survival when compared to microsatellite stable tumors.

Materials and Methods

We have retrospectively analyzed the cases of colon cancers treated in our institute for 3 years from 2017 to 2019. Most of the patients underwent surgery and received adjuvant chemotherapy. MSI testing was done in surgical specimen with immunohistochemistry. The clinical details of the patients were tabulated in Microsoft Excel, and statistical analysis was done using IBM SPSS Statistics for Windows, version 21 (IBM Corp., Armonk, NY, USA).

Results

A total of 52 patients who were treated in our institution from 2017 to 2019 were analyzed. The mean age was 46.8 ± 13.5 (19-72) years. The male-to-female ratio was 8:5. No significant association in patient demographics and clinicopathological parameters was observed between MSI stable and unstable disease. However, lymphovascular invasion showed a significantly higher trend in MSI unstable patients (P = 0.052). The median progression-free survival (PFS) of the entire cohort was 27.8 months (95% confidence interval = 22.7-32.9) and the median overall survival (OS) is not reached. The median PFS is 21.3 months in MSI stable patients whereas it is not reached in MSI unstable patients (P = 0.049). The median OS is 27.1 months in MSI stable patients, but it is not reached in MSI unstable patients and the difference shows a trend towards statistical significance (P = 0.061).

Conclusion

MSI unstable tumors were found to have higher PFS and higher OS in our study. It needs prospective validation in larger studies in Indian scenario.

Treatments after Immune Checkpoint Inhibitors in Patients with dMMR/MSI Metastatic Colorectal Cancer

Simple Summary

Several studies suggested an enhanced efficacy of conventional treatments (CT, i.e., chemotherapy +/− targeted therapy) administered after immune checkpoint inhibitors (ICI) in certain tumor types, but no data are available concerning metastatic colorectal cancer (mCRC) patients harboring mismatch repair deficiency/microsatellite instability (dMMR/MSI). The aim of our study was to assess the outcomes of dMMR/MSI mCRC patients receiving CT after ICI failure. We retrospectively collected clinical data from a multicentric cohort of 31 patients. Although limited by the small number of patients, our results did not suggest improved outcomes with CT in our population, and no significant association with previous ICI efficacy or with anti-VEGF agents was evidenced. However, prolonged disease control was observed in several cases, suggesting that some patients might derive an unexpected benefit from post-ICI treatments. With ICI becoming the standard of care in patients newly diagnosed with dMMR/MSI mCRC, these results might help to inform clinical decision-making and to guide future therapeutic strategies for these patients.

Abstract

Background: Several studies reported improved outcomes with conventional treatments (CT, i.e., chemotherapy ± targeted therapy) administered after immune checkpoints inhibitors (ICI) in certain tumor types. No data are available concerning patients (pts) with metastatic colorectal cancer (mCRC) harboring mismatch repair deficiency/microsatellite instability (dMMR/MSI). We aimed to assess the outcomes of dMMR/MSI mCRC pts receiving CT after ICI failure. Methods: We conducted a retrospective multicenter study investigating the outcomes of all dMMR/MSI mCRC pts who received post-ICI CT between 2015 and 2020. Results: 31 pts (male 61%, median age 56 years) were included. ICI was an anti-PD(L)1 monotherapy in 71% of pts, and 61% received >2 lines before post-ICI CT. The overall response rate and disease control rate were 13% and 45%, with a median progression-free survival (PFS) and overall survival of 2.9 and 7.4 months, respectively. No association of the outcomes with either ICI efficacy or anti-angiogenic agents was observed. Prolonged PFS (range 16.1–21.3 months) was observed in 4 pts (13%). Conclusions: Although conducted on a limited number of patients, our results do not support an association of previous ICI treatment with an enhanced efficacy of CT in dMMR/MSI mCRC. However, prolonged disease control was observed in several cases, suggesting that some pts might derive an unexpected benefit from post-ICI treatments.

High-Risk Features Are Prognostic in dMMR/MSI-H Stage II Colon Cancer

BACKGROUND

High-risk features, such as T4 disease, bowel obstruction, poorly/undifferentiated histology, lymphovascular, perineural invasion, and <12 lymph nodes sampled, indicate poor prognosis and define high-risk stage II disease in proficient mismatch repair stage II colon cancer (CC). The prognostic role of high-risk features in dMMR/MSI-H stage II CC is unknown. Similarly, the role of adjuvant therapy in high-risk stage II CC with dMMR/MSI-H (≥1 high-risk feature) has not been studied in prospective trials. The aim of this analysis of the National Cancer Database is to evaluate the prognostic value of high-risk features in stage II dMMR/MSI-H CC.

METHODS

Univariate (UVA) and multivariate (MVA) Cox proportional hazards (Cox-PH) models were built to assess the association between clinical and demographic characteristics and overall survival. Kaplan-Meier survival curves were generated with log-rank tests to evaluate the association between adjuvant chemotherapy in high-risk and low-risk cohorts separately.

RESULTS

A total of 2,293 stage II CC patients have dMMR/MSI-H; of those, 29.5% (n = 676) had high-risk features. The high-risk dMMR/MSI-H patients had worse overall survival [5-year survival and 95%CI, 73.2% (67.3-78.1%) vs. 80.3% (76.7-83.5%), p = 0.0001]. In patients with stage II dMMR/MSI-H CC, the high-risk features were associated with shorter overall survival (OS) along with male sex, positive carcinoembryonic antigen, Charlson-Deyo score >1, and older age. Adjuvant chemotherapy administration was associated with better OS, regardless of the high-risk features in dMMR/MSI-H (log-rank test, p = 0.001) or not (p = 0.0006). When stratified by age, the benefit of chemotherapy was evident only in patients age ≥65 with high-risk features.

CONCLUSION

High-risk features are prognostic in the setting of dMMR/MSI-H stage II CC. Adjuvant chemotherapy may improve survival specifically in patients ≥65 years and with high-risk features.

Sidedness determines clinical characteristics and survival outcomes in medullary adenocarcinoma of the colon

Colon medullary adenocarcinoma (MAC) is a rare histologic subtype. Clinical presentation and cancer outcomes of MAC, compared to colon adenocarcinoma (AC), remain incompletely described. Annual age-adjusted incidence rates were computed using Surveillance, Epidemiology, and End Results (2002–2017). A cohort analysis using the National Cancer Database (2010–2016) compared patient characteristics in an unmatched dataset and prognostic characteristics in a 1:1 matched subset. Reported annual age-adjusted incidence of MAC has significantly increased, with an average annual percent change (APC) increase of 23.8% (95% CI: 19.2–28.6); concurrent AC incidence declined (APC: − 2.8, 95% CI: − 3.1 to − 2.8). Analyses of 1018 MAC and 210,784 AC unmatched patients showed that MAC patients were more often older, female, and white, with higher disease stage, poorly-differentiated tumors, right-sided laterality, and lymphovascular invasion (all p < 0.0001). Among those with known microsatellite status, instability was more prevalent among MAC than AC patients (82% vs. 24%, p < 0.0001). Multivariate analyses of the matched dataset revealed that MAC histology was not independently associated with overall survival. However, when stratifying by laterality, left-sided MAC was associated with shorter survival when compared to right-sided MAC (HR 1.66, 95% CI 1.16–2.38) and right-sided AC (HR 1.54, 95% CI 1.12–2.12). The reported incidence of MAC is increasing, in contrast to the declining incidence of AC. MAC clinical and molecular features are distinct from AC and likely account for outcome differences. Overall, left-sided MAC was associated with the shortest OS. Molecular profiling may improve treatment guidelines for MAC.

The prognostic and predictive impact of BRAF mutations in deficient mismatch repair/microsatellite instability-high colorectal cancer: systematic review/meta-analysis

Aims: The authors present a systematic review/meta-analysis of the impact of BRAF mutations on prognosis and immune checkpoint inhibitor (ICI) response in deficient mismatch repair/microsatellite instability-high colorectal cancer. Methods: Hazard ratios for overall survival and odds ratios for objective response rate to ICIs were calculated in BRAF-mutated versus BRAF wild-type patients. Results: After screening, nine and three studies, respectively, were included for analysis of prognosis (analysis A) and ICI response (analysis B). Analysis A showed worse overall survival in BRAF-mutated compared with BRAF wild-type stage I-IV patients (hazard ratio: 1.57; 95% CI: 1.23-1.99), and analysis B showed no difference in objective response rate (odds ratio: 1.04; 95% CI: 0.48-2.25). Conclusion: BRAF mutations are associated with worse overall survival but not differential response to ICIs in deficient mismatch repair/microsatellite instability-high colorectal cancer.

Comparison of oncologic outcomes between patients with Lynch syndrome and sporadic microsatellite instability-high colorectal cancer

Purpose

Long-term oncologic differences in outcome between groups of patients with Lynch syndrome (LS) colorectal cancer (CRC) and sporadic CRC with microsatellite instability-high (MSI-H) are the focus of investigation in the current study.

Methods

Patients registered in the Korean Hereditary Tumor Registry and 2 tertiary referral hospitals treated for stage I–III CRC between 2005 and 2015 were retrospectively analyzed. Detection for both groups was performed using pedigree, microsatellite instability, and mismatch repair (MMR) gene testing. Multivariate analyses for overall survival (OS) and disease-free survival (DFS) were conducted.

Results

Cases of LS (n = 77) and sporadic CRC with MSI-H (n = 96) were identified. LS CRC patients were younger in age and displayed tumor sidedness, typically involving left-sided colon and rectum, compared to patients with sporadic CRC with MSI-H. OS and DFS were lower for LS CRC relative to CRC with MSI-H (OS, 72.7% vs. 93.8%, P = 0.001; DFS, 71.4% vs. 88.5%, P = 0.001). In multivariate analyses, tumor sidedness, stage, and chemotherapy were independent factors for OS and DFS. LS CRC was a prognostic factor for poorer OS (hazard ratio, 2.740; 95% confidence interval, 1.003–7.487; P = 0.049), but not DFS.

Conclusion

Our findings indicate that LS CRC is associated with poorer outcomes compared to sporadic CRC with MSI-H, presenting distinct clinical features. In view of the current lack of knowledge on genetic and molecular mechanisms, appropriate management taking into consideration the difficulty of identification of CRC with hypermutable tumors harboring heterogeneity is essential.

Cytoplasmic MSH2 Related to Genomic Deletions in the MSH2/EPCAM Genes in Colorectal Cancer Patients With Suspected Lynch Syndrome

Background

A large proportion of patients with Lynch syndrome (LS) have MSH2 abnormalities, but genotype-phenotype studies of MSH2 mutations in LS are still lacking. The aim of this study was to comprehensively analyze the clinicopathological characteristics and molecular basis of colorectal cancer (CRC) in patients with uncommon MSH2 cytoplasmic expression.

Methods

We retrospectively reviewed 4195 consecutive cases of CRC patients diagnosed between January 2015 and December 2017 at the Cancer Hospital Chinese Academy of Medical Sciences. Of the 4195 patients with CRC, 69 were indicated to have abnormal MSH2 expression through tumor immunohistochemical staining. Genetic tests, such as next-generation sequencing, large genomic rearrangement (LGR) analysis, microsatellite instability status analysis and genomic breakpoint analysis, were performed. Clinicopathological and molecular characteristics and clinical immunotherapy response were analyzed.

Results

Forty-five of 69 patients were identified to have LS with pathogenic germline mutations in MSH2 and/or EPCAM. Of these LS patients, 26.7% were confirmed to harbor large genomic rearrangements (LGRs). Of note, three tumors from two unrelated family pedigrees exhibited a rare cytoplasmic MSH2 staining pattern that was found in LS patients with EPCAM/MSH2 deletions. RNA analysis showed that two novel mRNA fusions of EPCAM and MSH2 resulted in the predicted protein fusion with MSH2 cytoplasmic localization. Analyses of genomic breakpoints indicated that two novel deletions of EPCAM and MSH2 originated from Alu repeat-mediated recombination events. Our study also provides clinical evidence for the beneficial effect of the PD-1 inhibitor pembrolizumab for CRC patients that exhibit cytoplasmic MSH2 staining.

Conclusion

Our study demonstrates that the rare cytoplasmic MSH2 staining pattern should be fully recognized by pathologists and geneticists. Given the specific genotype-phenotype correlation in LS screening, we advocate that all CRC patients with cytoplasmic MSH2 staining in histology should be screened for LGRs of EPCAM and MSH2.

Immune Checkpoint Inhibition in Metastatic Colorectal Cancer Harboring Microsatellite Instability or Mismatch Repair Deficiency

Simple Summary

Microsatellite instability (MSI) is a molecular indicator of defective DNA mismatch repair (dMMR). MSI/dMMR status is observed in approximately 5% of metastatic colorectal cancers (mCRC) but 10–18% of localized colorectal cancers. MSI/dMMR status is a major predictive biomarker for the efficacy of immune checkpoint inhibitors (ICIs). This review presents the current and future challenges of ICIs for patients with MSI/dMMR colorectal cancer.

Abstract

Microsatellite instability (MSI) is a tumor phenotype related to a deficient DNA mismatch repair system (dMMR). This phenotype, observed in 5% of metastatic mCRC but 10–18% of localized CRC, is associated with high tumor mutational burden with highly immunogenic neoantigens. It has emerged as a major predictive biomarker for the efficacy of ICIs. In this review, we will present a comprehensive overview of the literature concerning the efficacy of ICIs in MSI/dMMR mCRC, with a focus on new developments in first-line metastatic setting. Then, we will present current and future challenges of immuno-oncology for patients with MSI/dMMR metastatic CRC.

Immune Checkpoint Inhibition in Colorectal Cancer: Microsatellite Instability and Beyond

Immune checkpoints inhibitors (ICIs) have been a breakthrough, with unique response and survival patterns compared with chemotherapy for patients with advanced Mismatch Repair-deficient/Microsatellite instable (dMMR/MSI) colorectal cancer, but have shown disappointing results in Mismatch Repair-proficient/Microsatellite stable (pMMR/MSS) colorectal cancer. As up to 50% of patients harboring dMMR/MSI advanced cancers will ultimately progress after PD-1 blockade, biomarkers are needed to predict response/resistance to immunotherapy and to select patients for immunomodulating combination therapies. Patients with pMMR/MSS colorectal cancer present with distinct immune profiles compared to dMMR/MSI tumors, giving evidence of different immune escape mechanisms, which could be overcome through individualized immunotherapeutic strategies. In this review we discuss the latest developments in the field of immunotherapy for dMMR/MSI and pMMR/MSS colorectal cancers, and unresolved questions and considerations concerning the use of ICI therapies in this population. Future immunomodulation strategies based on biomarker selection (tumor mutational burden, Immunoscore^®, mutational profile) are discussed.

A review of the sensitivity of metastatic colorectal cancer patients with deficient mismatch repair to standard-of-care chemotherapy and monoclonal antibodies, with recommendations for future research

In 5% of metastatic colorectal cancer (mCRC) patients, tumours display a deficient mismatch repair (dMMR) system. Immunotherapy is beneficial in dMMR mCRC patients and has recently been approved by the Food and Drug Administration for patients with unresectable or metastatic dMMR CRC. Although dMMR and proficient MMR (pMMR) CRC tumours are biologically distinct, they are commonly treated with the same chemotherapy and monoclonal antibodies. This includes dMMR mCRC patients who did not respond to immunotherapy (20-30%). However, it is unclear if these treatments are equally beneficial in dMMR mCRC. Of note, dMMR mCRC patients have a worse prognosis compared to pMMR, which may in part be caused by a lower response to treatment. To avoid unnecessary exposure to ineffective treatments and their associated toxicity, it is important to identify which systemic treatments are most beneficial in dMMR mCRC patients, thus improving their outcome. Indeed, future treatment strategies are likely to involve combinations of immunotherapy, chemotherapy and monoclonal antibodies. In this evidence-based review, we summarize clinical trials reporting treatment efficacy of different types of chemotherapy and monoclonal antibodies in dMMR mCRC patients. We also review the biological rationale behind a potential differential benefit of chemotherapy with or without monoclonal antibodies in dMMR mCRC patients. A barrier in the interpretation of preclinical results is the choice of model systems. They largely comprise traditional models, including cell lines and xenografts, rather than more representative models, such as patient-derived organoids. We provide concrete recommendations for clinical investigators and fundamental researchers to accelerate research regarding which systemic therapy is most effective in dMMR mCRC patients.

The Role of Immune Checkpoint Inhibitors in Colorectal Adenocarcinoma

Over the past decade, immune checkpoint inhibitors (ICI) have proven to be promising agents in a number of solid tumor malignancies. Pembrolizumab and nivolumab are ICIs that target programmed cell death protein 1 and both have been approved by the US Food and Drug Administration for the treatment of microsatellite instability-high/DNA mismatch repair deficient (MSI-H/dMMR) colorectal cancer (CRC). In MSI-H/dMMR CRC, these agents were found to have considerable antitumor activity and are now used in the treatment of this disease. However, MSI-H/dMMR tumors account for only 5% of metastatic CRC and the remaining patients are identified as being microsatellite stable/DNA mismatch repair proficient (MSS/pMMR). In MSS/pMMR CRC, ICIs were found to have no antitumor activity and they are not currently used in the treatment of the disease. However, ongoing research is expanding our knowledge of how the human immune system interacts with cancer cells. Identifying mechanisms to improve our immune response to MSS/pMMR CRC is of utmost importance. In this review, we discuss available clinical data and the emerging role of immune-based strategies to overcome the resistance to ICI therapy in the treatment of MSS/pMMR CRC.

Comparison of long-term outcomes between Lynch sydrome and sporadic colorectal cancer: a propensity score matching analysis

Background

Lynch syndrome (LS) is the most common hereditary colorectal cancer (CRC) syndrome. Comparison of prognosis between LS and sporadic CRC (SCRC) were rare, with conflicting results. This study aimed to compare the long-term outcomes between patients with LS and SCRC.

Methods

Between June 2008 and September 2018, a total of 47 patients were diagnosed with LS by genetic testing at Fudan University Shanghai Cancer Center. A 1:2 propensity score matching was performed to obtain homogeneous cohorts from SCRC group. Thereafter, 94 SCRC patients were enrolled as control group. All of enrolled patients received curative surgeries and standardized postoperative monitoring. The long-term survival rates between the two groups were compared, and the prognostic factors were also analyzed.

Results

The 5-year overall survival rate of LS group was 97.6%, which was significantly higher than of 82.6% for SCRC group (χ² = 4.745, p = 0.029). The 5-year recurrence free survival rate showed no significant differences between the two groups (78.0% for LS group vs. 70.6% for SCRC patients; χ² = 1.260, p = 0.262). The 5-year tumor free survival rates in LS group was 62.1% for LS patients, which were significantly lower than of 70.6% for SCRC group (χ² = 4.258, p = 0.039). Subgroup analysis of recurrent patients show that the LS group had longer overall survival than the SCRC group after combined chemotherapy. By multivariate analysis, we found that tumor recurrence of primary CRC [Risk ratio (95% (confidence interval): 48.917(9.866–242.539); p < 0.001] and late TNM staging [Risk ratio (95% (confidence interval): 2.968(1.478–5.964); p = 0.002] were independent risk factors for OS.

Conclusion

LS patients have better long-term survival prognosis than SCRC patients, even though the two groups have statistically comparable recurrence free survival. Combined chemotherapy is an effective treatment for LS patients who developed primary CRC recurrence. Standardized postoperative monitoring for LS patients may enable detection of metachronous tumors at earlier stages, which was a guarantee of a favorable prognosis despite lower tumor free survival.

Redefining Colorectal Cancer by Tumor Biology

Colorectal cancer treatment has undergone a paradigm shift. We no longer see this disease as a singular, anatomic tumor type but rather a set of disease subgroups. Largely because of a better understanding of cancer biology and the introduction and integration of molecular biomarkers-the premise of precision therapy-we are beginning to direct treatments toward the right tumor target(s) in the right patients. The field of molecular profiling is continually evolving, and new biomarkers are constantly being discovered that have investigational, therapeutic, and/or prognostic implications-negative or positive. To date, only a few biomarkers have sufficient actionable, clinical implication to earn international guideline-recommended routine testing. Hence, it is vital that the treating oncologist should know which biomarkers to assess, when in the treatment course to test for them, and how the test is to be done. Correct interpretation of profiling results is imperative. Herein, we focus on international guideline-recommended mutation testing for patients prior to their colorectal cancer treatment initiation. The clinical applications of circulating tumor DNA (ctDNA) in patients with metastatic disease, based on our current knowledge and capabilities, are also addressed.

Development and validation of MMR prediction model based on simplified clinicopathological features and serum tumour markers

BACKGROUND

Although simplified clinicopathological features and serum tumour markers (STMs) were reported to be associated with the status of mismatch repair (MMR) in colorectal cancer (CRC) patients, their predictive value alone or in combination for MMR status remains unknown.

METHODS

A retrospective analysis of 3274 participants with MMR testing and STMs measurements from two institutions was conducted. The prediction model was developed in the primary cohort that consisted of 1964 participants. Best subset regression was applied to select the most useful predictors from the primary dataset. The performance of the nomogram was evaluated with respect to its calibration, discrimination, and clinical usefulness. External validation was performed in an independent validation cohort of 1310 consecutive CRC patients.

FINDINGS

Among the ten simplified clinicopathological features, seven variables were selected as the best subset of risk factors to develop pathology-based model, including age, tumour diameters, histology, tumour location, perineural invasion, the number of sampled lymph nodes (LNs) and positive LNs. The model showed good calibration and discrimination, with an AUC of 0.756 (95% CI, 0.722 to 0.789) in the primary cohort and 0.754 (95% CI, 0.715 to 0.793) in the validation cohort. After the addition of CEA and CA 72-4, the performance of pathology-based model was significantly improved in in both the primary cohort (AUC: 0.805 (0.774-0.835) vs. 0.756 (0.722-0.789), P < 0.001) and validation cohort (AUC: 0.796 (0.758-0.835) vs. 0.754 (0.715-0.793), P < 0.001). The results of decision curve analysis revealed that using our models to predict the status of MMR would add more benefit than either the detect-all-patients scheme or the detect-none scheme.

INTERPRETATION

The models based on simplified clinicopathological features alone or in combination with STMs can be conveniently used to facilitate the postoperative individualized prediction of MMR status in CRC patients.

Survival of patients with deficient mismatch repair metastatic colorectal cancer in the pre-immunotherapy era

Background

Metastatic colorectal cancer patients with deficient mismatch repair (dMMR mCRC) benefit from immunotherapy. Interpretation of the single-arm immunotherapy trials is complicated by insignificant survival data during systemic non-immunotherapy. We present survival data on a large, comprehensive cohort of dMMR mCRC patients, treated with or without systemic non-immunotherapy.

Methods

Two hundred and eighty-one dMMR mCRC patients (n = 54 from three prospective Phase 3 CAIRO trials; n = 227 from the Netherlands Cancer Registry). Overall survival was analysed from diagnosis of mCRC (OS), from initiation of first-line (OS1) and second-line (OS2) systemic treatment. Cox regression analysis examined prognostic factors. As comparison for OS 2746 MMR proficient mCRC patients were identified.

Results

Of 281 dMMR patients, 62% received first-line and 26% second-line treatment. Median OS was 16.0 months (13.8–19.6) with antitumour therapy and 2.5 months (1.8–3.5) in untreated patients. OS1 was 12.8 months (10.7–15.2) and OS2 6.2 months (5.4–8.9) in treated dMMR patients. Treated dMMR patients had a 7.6-month shorter median OS than pMMR patients.

Conclusion

Available data from immunotherapy trials lack a control arm with standard systemic treatment. Given the poor outcome compared to the immunotherapy results, our data strongly suggest a survival benefit of immunotherapy in dMMR mCRC patients.

Mismatch Repair System Genomic Scars in Gastroesophageal Cancers: Biology and Clinical Testing

Alterations in the mismatch repair (MMR) system result in genomic instability, neoantigen production, and immune response in cancer. There is evidence that gastroesophageal tumors with MMR deficiency may be susceptible to immune-checkpoint inhibitors treatment, especially in those presenting at advanced-stage disease. Although a number of biomarkers have been developed in histology-agnostic settings to assess MMR status, there is evidence that a tumor-specific testing approach would improve the selection of patients for immunotherapy. However, no testing methods have been developed specifically for gastroesophageal cancers so far. Here, we discuss the state of the art, current advances, and future perspectives of MMR-related biomarkers’ biologic and clinical role in gastroesophageal cancers.

DNA Mismatch Repair-Deficient Colorectal Carcinoma: Referral Rate for Genetic Cancer Risk Assessment in a Brazilian Cancer Center

BACKGROUND

Approximately 15% of colorectal cancers (CRCs) are deficient in DNA mismatch repair proteins (dMMR), a characteristic that can occur in both sporadic and hereditary CRC. Due to sparse studies on dMMR CRC in the Brazilian population, we conducted a retrospective analysis of referral rates for Genetic Cancer Risk Assessment of this population and also describing clinical and molecular characterization of these tumors.

METHODS

A retrospective, longitudinal, and unicenter study that included patients with dMMR CRC detected by IHC analysis from Pathology Database of our institution, from January 2015 to July 2017.

RESULTS

MMR IHC testing was performed in 998 CRC tumors, and 78 tumors (7.8%) had dMMR. The mean age at diagnosis was 56.8 years (17-90), and most patients were female (41 out of 78, 52.6%). Of the 52 patients with right-sided CRC, 40 tumors (77%) had loss of the MLH1 and/or PMS2 expression, and 12 tumors (23%) had loss of MSH2 and/or MSH6 expression (p = 0.005). From 78 patients with dMMR CRC, only 43 patients (55.1%) were referred for genetic counseling (GC), and of them, only 33 patients (76.7%) really went to GC consultation. A total of 21 patients with dMMR CRC performed genetic testing.

CONCLUSION

Overall, genetic referral was less than expected in our population. Most of dMMR CRC patients did not receive GC, even in a cancer center, either due to the absence of referral or personal decision and few patients who pursued genetic counseling performed genetic testing.

Exceptional Response to A Single Cycle of Immunotherapy in a Lynch Syndrome Patient with Metastatic Pancreatic Adenocarcinoma

Patient: Male, 65-year-old

Final Diagnosis: Lynch syndrome • pancreatic cancer

Symptoms: Abdominal pain • liver masses

Medication:—

Clinical Procedure: —

Specialty: Oncology

MLH1 Deficiency Induces Cetuximab Resistance in Colon Cancer via Her-2/PI3K/AKT Signaling

The rapid onset of resistance to cetuximab (CTX) limits its clinical utility in colorectal cancer (CRC) patients. This study aims to understand a potential role of mismatch repair gene mutL homolog 1 (MLH1) in CTX response. Functional analysis of MLH1 in Her-2/phosphoinositide 3-kinases (PI3K)/PKB protein kinase (AKT)-regulated CTX sensitivity is performed using human CRC specimens, CRC cell lines with different MLH1 expression levels, and a subcutaneous xenograft model. Overexpression, knockdown, small interfering RNA, and inhibitors are used to examine the role of MLH1 and HER-2 downstream signaling and apoptotic targets in CTX sensitivity. Reduced MLH1 expression is correlated with unfavorable prognosis in cetuximab-treated patients. MLH1 loss decreases CTX sensitivity through Her-2/PI3K/AKT signaling and apoptosis resistance in culture and in xenografts, while MLH1 overexpression increases CTX sensitivity. Blocking Her-2 signaling increases CTX sensitivity of microsatellite instability CRC in vitro and in vivo. MLH1 loss induces activation of Her-2/PI3K/AKT signaling and leads to cetuximab resistance in colon cancer.

Cancer Genetic Counseling-Current Practice and Future Challenges

Cancer genetic counseling practice is rapidly evolving, with services being provided in increasingly novel ways. Pretest counseling for cancer patients may be abbreviated from traditional models to cover the elements of informed consent in the broadest of strokes. Genetic testing may be ordered by a cancer genetics professional, oncology provider, or primary care provider. Increasingly, direct-to-consumer testing options are available and utilized by consumers anxious to take control of their genetic health. Finally, genetic information is being used to inform oncology care, from surgical decision-making to selection of chemotherapeutic agent. This review provides an overview of the current and evolving practice of cancer genetic counseling as well as opportunities and challenges for a wide variety of indications in both the adult and pediatric setting.

Molecular Analyses of Left- and Right-Sided Tumors in Adolescents and Young Adults with Colorectal Cancer

BACKGROUND

The incidence of colorectal cancer (CRC), particularly left-sided tumors (LT), in adolescents and young adults (AYA) is rising. Epigenetic events appear to play an important role in tumorigenesis and cancer progression, especially in younger patients. We compared molecular features of LT to right-sided tumors (RT) in AYA.

MATERIALS AND METHODS

A total of 246 LT and 56 RT were identified in a cohort of 612 AYA with primary CRC. Tumors were examined by next-generation sequencing (NGS), protein expression, and gene amplification. Tumor mutational burden (TMB) and microsatellite instability (MSI) were determined based on NGS data.

RESULTS

RT showed higher mutation rates compared with LT in several genes including BRAF (10.3% vs. 2.8%), KRAS (64.1% vs. 45.5%), PIK3CA (27% vs. 11.2%), and RNF43 (24.2% vs. 2.9%). Notably, additional mutations in distinct genes involved in histone modification and chromatin remodeling, as well as genes associated with DNA repair and cancer-predisposing syndromes, were characteristic of RT; most frequently KMT2D (27.8% vs. 3.4%), ARID1A (53.3% vs. 21.4%), MSH6 (11.1% vs. 2.3%), MLH1 (10.5% vs. 2.3%), MSH2 (10.5% vs. 1.2%), POLE (5.9% vs. 0.6%), PTEN (10.8% vs. 2.3%), and BRCA1 (5.4% vs. 0.6%). MSI was seen in 20.8% of RT versus 4.8% of LT. RT had a higher frequency of TMB-high regardless of MSI status.

CONCLUSION

Molecular profiling of AYA CRC revealed different molecular characteristics in RT versus LT. Epigenetic mechanisms and alteration in DNA repair genes warrant further investigation and may be a promising treatment target for CRC in AYA.

IMPLICATIONS FOR PRACTICE

Colorectal cancer (CRC) in adolescents and young adults (AYA) comprises a distinct entity with different clinicopathologic features and prognosis compared with older patients. Molecular profiling of right- and left-sided tumors in AYA is needed to gain novel insight into CRC biology and to tailor targeted treatment in this age group. This study found that right- and left-sided CRC show distinct molecular features in AYA, overall and in subgroups based on microsatellite instability status. Alterations in DNA double-strand break repair and homologous recombination repair, as well as epigenetic mechanisms, appear to play a critical role. The present molecular profiling data may support the development of personalized treatment strategies in the AYA population.

Prognosis and chemosensitivity of deficient MMR phenotype in patients with metastatic colorectal cancer: An AGEO retrospective multicenter study

Mismatch repair-deficient (dMMR) and/or microsatellite instability-high (MSI) colorectal cancers (CRC) represent about 5% of metastatic CRC (mCRC). Prognosis and chemosensitivity of dMMR/MSI mCRC remain unclear. This multicenter study included consecutive patients with dMMR/MSI mCRC from 2007 to 2017. The primary endpoint was the progression-free survival (PFS) in a population receiving first-line chemotherapy. Associations between chemotherapy regimen and survival were evaluated using a Cox regression model and inverse of probability of treatment weighting (IPTW) methodology in order to limit potential biases. Overall, 342 patients with dMMR/MSI mCRC were included. Median PFS and overall survival (OS) on first-line chemotherapy were 6.0 and 26.3 months, respectively. For second-line chemotherapy, median PFS and OS were 4.4 and 21.6 months. Longer PFS (8.1 vs. 5.4 months, p = 0.0405) and OS (35.1 vs. 24.4 months, p = 0.0747) were observed for irinotecan-based chemotherapy compared to oxaliplatin-based chemotherapy. The association was no longer statistically significant using IPTW methodology. In multivariable analysis, anti-VEGF as compared to anti-EGFR was associated with a trend to longer OS (HR = 1.78, 95% CI 1.00-3.19, p = 0.0518), whatever the backbone chemotherapy used. Our study shows that dMMR/MSI mCRC patients experienced short PFS with first-line chemotherapy with or without targeted therapy. OS was not different according to the chemotherapy regimen used, but a trend to better OS was observed with anti-VEGF. Our study provides some historical results concerning chemotherapy in dMMR/MSI mCRC in light of the recent nonrandomized trials with immune checkpoint inhibitors.

Biomarker-guided therapy for colorectal cancer: strength in complexity

The number of molecularly stratified treatment options available to patients with colorectal cancer (CRC) is increasing, with a parallel rise in the use of biomarkers to guide prognostication and treatment decision-making. The increase in both the number of biomarkers and their use has resulted in a progressively complex situation, evident both from the extensive interactions between biomarkers and from their sometimes complex associations with patient prognosis and treatment benefit. Current and emerging biomarkers also reflect the genomic complexity of CRC, and include a wide range of aberrations such as point mutations, amplifications, fusions and hypermutator phenotypes, in addition to global gene expression subtypes. In this Review, we provide an overview of current and emerging clinically relevant biomarkers and their role in the management of patients with CRC, illustrating the intricacies of biomarker interactions and the growing treatment opportunities created by the availability of comprehensive molecular profiling.

Mechanisms of immunogenicity in colorectal cancer

Background

The immune response in cancer is increasingly understood to be important in determining clinical outcomes, including responses to cancer therapies. New insights into the mechanisms underpinning the immune microenvironment in colorectal cancer are helping to develop the role of immunotherapy and suggest targeted approaches to the management of colorectal cancer at all disease stages.

Method

A literature search was performed in PubMed, MEDLINE and Cochrane Library databases to identify relevant articles. This narrative review discusses the current understanding of the contributors to immunogenicity in colorectal cancer and potential applications for targeted therapies.

Results

Responsiveness to immunotherapy in colorectal cancer is non-uniform. Several factors, both germline and tumour-related, are potential determinants of immunogenicity in colorectal cancer. Current approaches target tumours with high immunogenicity driven by mutations in DNA mismatch repair genes. Recent work suggests a role for therapies that boost the immune response in tumours with low immunogenicity.

Conclusion

With the development of promising therapies to boost the innate immune response, there is significant potential for the expansion of the role of immunotherapy as an adjuvant to surgical treatment in colorectal cancer.

Consequences of a high incidence of microsatellite instability and BRAF-mutated tumors: A population-based cohort of metastatic colorectal cancer patients

Background

Immunotherapy for patients with microsatellite‐instable (MSI‐H) tumors or BRAF‐inhibitors combination treatment for BRAF‐mutated (mutBRAF) tumors in metastatic colorectal cancer (mCRC) is promising, but the frequency of these molecular changes in trial patients are low. Unselected population‐based studies of these molecular changes are warranted.

Methods

A population‐based cohort of 798 mCRC patients in Scandinavia was studied. Patient and molecular tumor characteristics, overall survival (OS) and progression‐free survival (PFS) were estimated.

Results

Here, 40/583 (7%) tumor samples were MSI‐H and 120/591 (20%) were mutBRAF; 87% of MSI‐H tumors were mutBRAF (non‐Lynch). Elderly (>75 years) had more often MSI‐H (10% vs 6%) and MSI‐H/mutBRAF (9% vs 4%) tumors. Response rate (5% vs 44%), PFS (4 vs 8 months), and OS (9 vs 18 months) after first‐line chemotherapy was all significantly lower in patients with MSI‐H compared to patients with microsatellite stable tumors. MSI‐H and mutBRAF were both independent poor prognostic predictors for OS (P = 0.049, P < 0.001) and PFS (P = 0.045, P = 0.005) after first‐line chemotherapy. Patients with MSI‐H tumors received less second‐line chemotherapy (15% vs 37%, P = 0.005).

Conclusions

In unselected mCRC patients, MSI‐H and mutBRAF cases were more common than previously reported. Patients with MSI‐H tumors had worse survival, less benefit from chemotherapy, and they differed considerably from recent third‐line immunotherapy trial patients as they were older and most had mutBRAF tumor (non‐Lynch).

Methylation and expression analysis of mismatch repair genes in extramammary Paget's disease

BACKGROUND

Extramammary Paget's disease (EMPD) is a rare skin cancer with relative high frequencies of germline and somatic mismatch repair (MMR) genes mutations. However, the methylation and expression of these genes have not been validated in EMPD.

OBJECTIVE

This study aims to confirm the methylation and expression of MMR genes in EMPD.

METHODS

Immunohistochemical (IHC) staining detection and Methylation-specific PCR (MSP) were used to analyse MLH1, MSH2, MSH6 and PMS2 proteins' expression and promoters' methylation in 57 EMMD samples, and pyro-sequence was used to find highly methylated CpG sites in MSH2 promoter.

RESULTS

Immunohistochemical detection displayed reduced expression of MSH2 in 38.6% EMPD cases but normal expression of MLH1, MSH6 and PMS2 in all tumour tissues. Hypermethylation also was found in the promoter of MSH2 but not in other MMR genes. Pyrosequencing of MSH2 promoter showed CpG6 (-87) and CpG3 (-98) were the most common two methylated CpG dinucleotides. There is a significant correlation between reduced MSH2 expression and MSH2 methylation.

CONCLUSION

Reduced MSH2 expression and hypermethylation in this gene promoter were common genetic changes in EMPD, which expands our understanding of the role of MMR function in this skin cancer.

Stratification of patients with colorectal cancer without the recorded family history

Colorectal cancer (CRC) is a multifactorial disease and one of the most malignant tumours. In addition to the sporadic form, familial occurrences, particularly hereditary non-polyposis CRC-Lynch syndrome (LS)-are often observed. LS is caused by a germline mutation in mismatch repair (MMR) genes, whose task it is to correct errors in the DNA structure that result from its replication. The aim of the present study was to stratify CRC patients using molecular diagnostics and next generation sequencing, according to the chosen criteria [positive for microsatellite instability (MSI) and negative for a BRAF mutation and MutL homolog 1 (MLH1) methylation], and subsequently to detect pathological germline mutations in MMR genes in Slovak patients. To exclude patients with MSI from further testing, the present study detected the BRAF V600E mutation and examined MLH1 methylation status. From the 300 CRC patients, 37 cases with MSI were identified. In the MSI-positive samples, 13 cases of BRAF V600E mutation were recorded. In 24 BRAF-negative patients, 11 cases of epigenetic methylation of MLH1 and 12 cases without MLH1 methylation suspected for LS were detected, and it was not possible to analyse the methylation phenotype of 1 sample. Thus, the present study reports the novel deletion of four nucleotides, 1627_1630del AAAG (Glu544Lysfs*26) in MSH6, probably associated with LS. A second case with a nonsense mutation in MSH was also detected, namely MMR_c.1030C>T (p.Q344X).

[Epidemiology of microsatellite instability across solid neoplasms]

Microsatellite instability (MSI) is a predictive biomarker for the efficacy of immune checkpoint inhibitors, regardless of the tumor type. While clinical characteristics of MSI cancer patients have been largely described in tumor localizations frequently associated with this genetic phenotype (i.e. colorectal cancer, endometrial cancer), it remains poorly characterized in other neoplasms. Pan-tumor high-throughput genome sequence analyses have contributed to the broadening of knowledge about the landscape of MSI. This review aims at synthetizing the literature concerning the frequency of MSI status in solid cancers, according to the cancer stage and the hereditary or sporadic origin of the mismatch repair deficiency. We then check for other cancers frequently associated with MSI and describe the clinical and pathological characteristics that should suggest a MSI phenotype.

A gene expression assay for simultaneous measurement of microsatellite instability and anti-tumor immune activity

Background

Clinical benefit from checkpoint inhibitors has been associated in a tumor-agnostic manner with two main tumor traits. The first is tumor antigenicity, which is typically measured by tumor mutation burden, microsatellite instability (MSI), or Mismatch Repair Deficiency using gene sequence platforms and/or immunohistochemistry. The second is the presence of a pre-existing adaptive immune response, typically measured by immunohistochemistry (e.g. single analyte PD-L1 expression) and/or gene expression signatures (e.g. tumor “inflamed” phenotype). These two traits have been shown to provide independent predictive information. Here we investigated the potential of using gene expression to predict tumor MSI, thus enabling the measurement of both tumor antigenicity and the level of tumor inflammation in a single assay, possibly reducing sample requirement, turn-around time, and overall cost.

Methods

Using The Cancer Genome Atlas RNA-seq datasets with the greatest MSI-H incidence, i.e. those from colon (n = 208), stomach (n = 269), and endometrial (n = 241) cancers, we trained an algorithm to predict tumor MSI from under-expression of the mismatch repair genes MLH1, PMS2, MSH2, and MSH6 and from 10 additional genes with strong pan-cancer associations with tumor hypermutation. The algorithms were validated on the NanoString nCounter™ platform in independent cohorts of colorectal (n = 52), endometrial (n = 11), and neuroendocrine (n = 4) tumors pre-characterized using the MMR immunohistochemistry assay.

Results

In the validation cohorts, the algorithm showed high prediction accuracy of tumor MSI status, with sensitivity of at least 88% attained at thresholds chosen to achieve 100% specificity. Furthermore, MSI status was compared to the Tumor Inflammation Signature (TIS), an analytically validated diagnostic assay which measures a suppressed adaptive immune response in the tumor and enriches for response to immune checkpoint blockade. TIS score was largely independent of MSI status, suggesting that measuring both parameters may identify more patients that would respond to immune checkpoint blockade than either assay alone.

Conclusions

Development of a gene expression signature of MSI status raises the possibility of a combined diagnostic assay on a single platform which measures both tumor antigenicity and presence of a suppressed adaptive immune response. Such an assay would have significant advantages over multi-platform assays for both ease of use and turnaround time and could lead to a diagnostic test with improved clinical performance.

Electronic supplementary material

The online version of this article (10.1186/s40425-018-0472-1) contains supplementary material, which is available to authorized users.