Mismatch repair–deficient colorectal cancer: a model of immunogenic and immune cell–rich tumor despite nonsignificant programmed cell death ligand-1 expression in tumor cells

Effect of RAS mutations and related immune characteristics on the prognosis of patients with MSI-H/dMMR colorectal cancer

PURPOSE

Microsatellite high instability/deficient mismatch repair (MSI-H/dMMR) colorectal cancer (CRC) has an active tumor microenvironment, rendering it more sensitive to immune checkpoint inhibitors. Given that studies involving patients with MSI-H colorectal cancer with RAS mutations are scarce, we explored the effect of RAS mutations on the TME in patients with MSI-H/dMMR cancer and identified potential prognostic factors.

METHODS

Seventy-five patients diagnosed with MSI-H/dMMR colorectal cancer were retrospectively enrolled and divided into RAS-mutant and -wild-type groups. The expression levels of CD11c+ dendritic cells, CD4+ T cells, CD8+ T cells, and regulatory T cell (Treg) markers were detected, and prognostic factors were analyzed.

RESULTS

RAS-mutant MSI-H colorectal patients were more likely to have: (1) higher platelet values; (2) shorter disease-free survival (DFS); (3) lower infiltrated numbers of CD11c+ dendritic cells, CD4+ T lymphocytes, and CD8+ T lymphocytes, and higher infiltrated numbers of Foxp3+ Treg cells. In MSI-H/dMMR CRC patients: (1) the high CD11c + , CD4 +,  and CD8 +  cells infiltration group had longer DFS than the low-infiltration group, and Foxp3 + cells infiltration was not significantly correlated with DFS; (2) the RAS mutation status, number of CD11c+ cells infiltrated, and carbohydrate antigen 19-9 (CA19-9) level were the potential prognostic factors.

CONCLUSION

RAS mutations in patients with MSI-H/dMMR CRC may reduce the infiltration of CD11c+ dendritic cells, CD4+ T cells, and CD8+ T cells, and increase the infiltration of Foxp3+ Treg cells to affect the tumor microenvironment of patients. RAS gene status, CD11c + cells infiltration, and CA19-9 level were potential prognostic factors for MSI-H/dMMR CRC.

The characteristics of the tumor immune microenvironment in colorectal cancer with different MSI status and current therapeutic strategies

Colorectal cancer (CRC) remains a significant cause of cancer-related mortality worldwide. Despite advancements in surgery, chemotherapy, and radiotherapy, the effectiveness of these conventional treatments is limited, particularly in advanced cases. Therefore, transition to novel treatment is urgently needed. Immunotherapy, especially immune checkpoint inhibitors (ICIs), has shown promise in improving outcomes for CRC patients. Notably, patients with deficient mismatch repair (dMMR) or microsatellite instability-high (MSI-H) tumors often benefit from ICIs, while the majority of CRC cases, which exhibit proficient mismatch repair (pMMR) or microsatellite-stable (MSS) status, generally show resistance to this approach. It is assumed that the MSI phenotype cause some changes in the tumor microenvironment (TME), thus triggering antitumor immunity and leading to response to immunotherapy. Understanding these differences in the TME relative to MSI status is essential for developing more effective therapeutic strategies. This review provides an overview of the TME components in CRC and explores current approaches aimed at enhancing ICI efficacy in MSS CRC.

Clinicopathological and immune characterization of mismatch repair deficient endocervical adenocarcinoma

Endocervical adenocarcinoma (ECA) is reported increasingly often in young women, and this aggressive disease lacks effective methods of targeted therapy. Since mismatch repair deficiency (dMMR) is an important biomarker for predicting response to immune checkpoint inhibitors, it is important to investigate the clinicopathological features and immune microenvironment of dMMR ECAs. We assessed 617 ECAs from representative tissue microarray sections, gathered clinicopathologic information, reviewed histological characteristics, and performed immunohistochemical staining for MMR, programmed cell death 1 (PD-L1), and other immune markers. Of 617 ECA samples, 20 (3.2%) cases had dMMR. Among them, loss of MMR-related proteins expression was observed in 17/562 (3.0%) human papilloma virus-associated (HPVA) adenocarcinoma and 3/55 (5.5%) non-HPV-associated (NHPVA) adenocarcinoma. In NHPVA cohort, dMMR status was observed in 3 (3/14, 15.0%) patients with clear cells. dMMR ECAs had a higher tendency to have a family history of cancer, larger tumor size, p16 negative, HPV E6/E7 mRNA in situ hybridization (HPV E6/E7 RNAscope) negative, and lower ki-67 index. Among the morphological variables evaluated, poor differentiation, necrosis, stromal tumor-infiltrating lymphocytes, peritumoral lymphocytes, and lymphoid follicles were easily recognized in the dMMR ECAs. In addition, dMMR ECAs had higher CD3+, CD8+, CD38+, CD68+ and PD-1+ immune cells. A relatively high prevalence of PD-L1 expression was observed in dMMR ECAs. dMMR ECAs were significantly more likely to present with a tumor-infiltrating lymphocytes -high/PD-L1-positive status. In conclusion, dMMR ECAs have some specific morphological features and a critical impact on the immune microenvironment, which may provide insights into improving responses to immunotherapy-included comprehensive treatment for ECAs in the future.

Prevalence and Associations of Beta2-Microglobulin Mutations in MSI-H/dMMR Cancers

Microsatellite instability (MSI) has emerged as an important predictor of sensitivity for immunotherapy-based strategies. β-2-Microglobulin (B2M) contains microsatellites within the coding regions and is prone to somatic changes in MSI/mismatch repair deficiency (MSI/dMMR) tumors. To delineate prevalence and associations of B2M mutations in MSI-H/dMMR cancers, we investigated the mutational profile of B2M and clinical and pathological features in gastric cancer (GC), colorectal cancer (CRC), and endometrial cancer (EC) with a high incidence of microsatellite instability-high (MSI-H)/dMMR. Formalin-fixed paraffin-embedded (FFPE) tumor tissues along with matched normal tissues were collected from 108 MSI/dMMR patients with GC, CRC, and EC. Genomic profiling of tissue and blood samples were assessed next-generation sequencing (NGS). Immunohistochemistry (IHC) was used to examine the presence or absence of B2M protein. Alternations in the exonic microsatellite regions of B2M were observed at various but high frequencies (57.5% in CRC, 23.9% in GC, and 13.6% in EC) and in different forms. NGS assay revealed that genes involved in chromatin regulation, the PI3K pathway, the WNT pathway, and mismatch repair were extensively altered in the MSI-H cohort. Signature 6 and 26, 2 of 4 mutational signatures associated with defective DNA mismatch repair, featured with high numbers of small insertion/deletions (INDEL) dominated in all 3 types of cancer. Alternations in the exonic microsatellite regions of B2M were observed at various but high frequencies (57.5% in CRC, 23.9% in GC, and 13.6% in EC) and in different forms. Tumor mutational burden (TMB) was significantly higher in the patients carrying MSI-H/dMMR tumors with B2M mutation than that in patients with wild-type B2M (P = .026).The frame shift alteration occurring at the exonic microsatellite sties caused loss of function of B2M gene. In addition, a case with CRC carrying indels in B2M gene resisted the ICI treatment was reported. In conclusion, patients carrying MSI-H/dMMR tumors with B2M mutation showed significantly higher TMB. Prescription of ICIs should be thoroughly evaluated for these patients.

Checkpoint molecules on infiltrating immune cells in colorectal tumor microenvironment

Colorectal cancer (CRC) is one of the most prevalent cancer types worldwide, with a high mortality rate due to metastasis. The tumor microenvironment (TME) contains multiple interactions between the tumor and the host, thus determining CRC initiation and progression. Various immune cells exist within the TME, such as tumor-infiltrating lymphocytes (TILs), tumor-associated macrophages (TAMs), and tumor-associated neutrophils (TANs). The immunotherapy approach provides novel opportunities to treat solid tumors, especially toward immune checkpoints. Despite the advances in the immunotherapy of CRC, there are still obstacles to successful treatment. In this review, we highlighted the role of these immune cells in CRC, with a particular emphasis on immune checkpoint molecules involved in CRC pathogenesis.

Tumor-Infiltrating Lymphocytes in Colorectal Cancer: The Fundamental Indication and Application on Immunotherapy

The clinical success of immunotherapy has revolutionized the treatment of cancer patients, bringing renewed attention to tumor-infiltrating lymphocytes (TILs) of various cancer types. Immune checkpoint blockade is effective in patients with mismatched repair defects and high microsatellite instability (dMMR-MSI-H) in metastatic colorectal cancer (CRC), leading the FDA to accelerate the approval of two programmed cell death 1 (PD-1) blocking antibodies, pembrolizumab and nivolumab, for treatment of dMMR-MSI-H cancers. In contrast, patients with proficient mismatch repair and low levels of microsatellite stability or microsatellite instability (pMMR-MSI-L/MSS) typically have low tumor-infiltrating lymphocytes and have shown unsatisfied responses to the immune checkpoint inhibitor. Different TILs environments reflect different responses to immunotherapy, highlighting the complexity of the underlying tumor-immune interaction. Profiling of TILs fundamental Indication would shed light on the mechanisms of cancer-immune evasion, thus providing opportunities for the development of novel therapeutic strategies. In this review, we summarize phenotypic diversities of TILs and their connections with prognosis in CRC and provide insights into the subsets-specific nature of TILs with different MSI status. We also discuss current clinical immunotherapy approaches based on TILs as well as promising directions for future expansion, and highlight existing clinical data supporting its use.

Durable complete response to pembrolizumab in microsatellite stable colorectal cancer

INTRODUCTION

Immunotherapy by checkpoint inhibitors, i.e., anti-programmed death-1(PD-1) or anti-programmed death-ligand 1 (PD-L1) antibodies, has gained more attention managing solid tumors. Pembrolizumab (an anti-PD-1 antibody) in metastatic colorectal cancer (CRC) was approved in 2017 by the US FDA.

REASON FOR THE REPORT

Pembrolizumab is not effective in microsatellite stable, mismatch-repair-proficient (MSS-pMMR) molecular phenotype, which comprises most CRC patients. In this report, we present the first case of metastatic CRC with a dramatic and durable response to pembrolizumab despite being of MSS-pMMR phenotype. A 34-year-old woman, presented seven years ago with T3N2bM0 colon cancer and an appendix carcinoid tumor. The last relapse with bilateral pulmonary metastases was refractory to all treatments. Although it seemed unresponsive to immunotherapy because of MSS molecular phenotype, due to the high expression level of PD-L1 (85%), we started treatment with pembrolizumab 200 mg every three weeks and continued for the overall 19 courses. Surprisingly, a rapid and complete response was observed that last until now, i.e., 17 months after discontinuation of pembrolizumab.

OUTCOME

Despite non-promising results in the current clinical trials, MSS-pMMR colorectal cancer patients' deprivation from immunotherapy seems not to be reasonable. There are ongoing clinical trials on checkpoint inhibitors either alone or in combination with other drugs. However, immunostaining for PD-L1 should be considered as a possible response predictor. Immunotherapy either by cell-based approaches or by checkpoint inhibitors may revolutionize cancer treatment Pembrolizumab has been approved by the FDA in 2017 for colorectal cancer. However, MSS-pMMR molecular phenotype which comprises the majority of CRC patients, has not shown a good response to checkpoint inhibitors. We present a MSS-pMMR case with complete and durable response to pembrolizumab We suggest immunostaining for PD-L1 as a possible response predictor to checkpoint inhibitors.

Programmed death-ligand 1 expression in the tumour stroma of colorectal liver oligometastases and its association with prognosis after liver resection

Background

The clinical value of programmed death-ligand 1 (PD-L1) expression in colorectal liver oligometastases (CLOs) remains undefined. This study aimed to detect PD-L1 in the microenvironment of CLOs and determine its association with patient prognosis.

Methods

We collected 126 liver-resection specimens from CLO patients who underwent curative liver resection between June 1999 and December 2016. Immunohistochemistry (IHC) was performed to assess PD-L1 expression in paraffin-embedded specimens. Overall survival (OS) and recurrence-free survival (RFS) were analysed using the Kaplan–Meier method and log-rank test.

Results

PD-L1 was mainly expressed in the stroma of liver oligometastases. Patients with high PD-L1 expression had a higher proportion of clinical-risk scores (CRSs) of 2–4 (67.7% vs 40.4%; P = 0.004). With a median 58-month follow-up, patients with high PD-L1 expression had a significantly lower 3-year OS rate (65.5% vs 92.7%; P = 0.001) and 3-year RFS rate (34.7% vs 83.8%; P < 0.001) than patients with low PD-L1 expression. Multivariate Cox analysis demonstrated that high PD-L1 expression (hazard ratio [HR] = 3.581; 95% confidence interval [CI] 2.301–9.972; P = 0.015), CRS 2–4 (HR = 6.960; 95% CI 1.135–42.689; P = 0.036) and increased preoperative CA19-9 (HR = 2.843; 95% CI 1.229–6.576; P = 0.015) were independent risk factors for OS. High PD-L1 expression (HR = 4.815; 95% CI 2.139–10.837; P < 0.001) and lymph-node metastasis (HR = 2.115; 95% CI 1.041–4.297; P = 0.038) were independent risk factors for RFS.

Conclusion

This study found that PD-L1 was commonly expressed in the tumour stroma of CLOs and high PD-L1 expression was associated with poor prognosis.

MSI-High RAS-BRAF wild-type colorectal adenocarcinomas with MLH1 loss have a high frequency of targetable oncogenic gene fusions whose diagnoses are feasible using methods easy-to-implement in pathology laboratories

Targetable kinase fusions are extremely rare (<1%) in colorectal cancers (CRCs), making their diagnosis challenging and often underinvestigated. They have been shown particularly frequently among MSI-High, BRAF/KRAS/NRAS wild-type CRCs with MLH1 loss (MLH1^loss MSI-High wild-type). We searched for NTRK1, NTRK2, NTRK3, ALK, ROS1, BRAF, RET, and NRG1 kinase fusions in CRCs using methods easy-to-implement in pathology laboratories: immunohistochemistry (IHC), fluorescent in situ hybridization (FISH), and fully automated real-time PCR targeted analyses. RNA-sequencing analyses were used for confirmation. Among 84 selected MLH1 deficient (IHC) CRCs cases, MLH1^loss MSI-High wild-type CRCs consisted first in 19 cases after Idylla™ analyses and finally in 18 cases (21%) after RNA-sequencing (detection of one additional KRASG12D mutation). FISH (and when relevant, IHC) analyses concluded in 5 NTRK1, 3 NTRK3, 1 ALK, 2 BRAF, and 2 RET FISH positive tumors. ALK and NTRK1 rearranged tumors were IHC positive, but pan-TRK IHC was negative in the 3 NTRK3 FISH positive tumors. RNA-sequencing analyses confirmed 12 of 13 fusions with only one false positive RET FISH result. Finally, 12/18 (67%) of MLH1^loss MSI-High wild-type CRCs contained targetable kinase fusions. Our study demonstrates the feasibility, but also the cost-effectiveness, of a multistep but rapid diagnostic strategy based on nonsequencing methods to identify rare and targetable kinase fusions in patients with advanced CRCs, as well as the high prevalence of these kinase fusions in MLH1^loss MSI-High wild-type CRCs. Nevertheless, confirmatory RNA-sequencing analyses are necessary in case of low FISH positive nuclei percentage to rule out FISH false-positive results.

The Mechanisms Leading to Distinct Responses to PD-1/PD-L1 Blockades in Colorectal Cancers With Different MSI Statuses

Current clinical studies showed distinct therapeutic outcomes, in which CRC patients with mismatch repair-deficient (dMMR)/microsatellite instability high (MSI-H) seem to be relatively more "sensitive" in response to anti-programmed death-1 receptor (PD-1)/programmed death-1 receptor ligand 1 (PD-L1) therapy than those with mismatch repair-proficient (pMMR)/microsatellite instability-low (MSI-L). The mechanisms by which the same PD-1/PD-L1 blockades lead to two distinct therapeutic responses in CRC patients with different MSI statuses remain poorly understood and become a topic of great interest in both basic research and clinical practice. In this review of the potential mechanisms for the distinct response to PD-1/PD-L1 blockades between dMMR/MSI-H CRCs and pMMR/MSI-L CRCs, relevant references were electronically searched and collected from databases PubMed, MEDLINE, and Google scholar. Sixty-eight articles with full text and 10 articles by reference-cross search were included for final analysis after eligibility selection according to the guidelines of PRISMA. Analysis revealed that multiple factors e.g. tumor mutation burden, immune cell densities and types in the tumor microenvironment, expression levels of PD-1/PD-L1 and cytokines are potential determinants of such distinct response to PD-1/PD-L1 blockades in CRC patients with different MSI statuses which might help clinicians to select candidates for anti-PD-1/PD-L1 therapy and improve therapeutic response in patients with CRC.

Personalized Medicine-Current and Emerging Predictive and Prognostic Biomarkers in Colorectal Cancer

Colorectal cancer (CRC) is the third most common cancer diagnosed worldwide and is heterogeneous both morphologically and molecularly. In an era of personalized medicine, the greatest challenge is to predict individual response to therapy and distinguish patients likely to be cured with surgical resection of tumors and systemic therapy from those resistant or non-responsive to treatment. Patients would avoid futile treatments, including clinical trial regimes and ultimately this would prevent under- and over-treatment and reduce unnecessary adverse side effects. In this review, the potential of specific biomarkers will be explored to address two key questions—1) Can the prognosis of patients that will fare well or poorly be determined beyond currently recognized prognostic indicators? and 2) Can an individual patient’s response to therapy be predicted and those who will most likely benefit from treatment/s be identified? Identifying and validating key prognostic and predictive biomarkers and an understanding of the underlying mechanisms of drug resistance and toxicity in CRC are important steps in order to personalize treatment. This review addresses recent data on biological prognostic and predictive biomarkers in CRC. In addition, patient cohorts most likely to benefit from currently available systemic treatments and/or targeted therapies are discussed in this review.

Microsatellite instability diagnosis using the fully automated Idylla platform: feasibility study of an in-house rapid molecular testing ancillary to immunohistochemistry in pathology laboratories

Aim

To study the performances of the Idylla MSI Assay in the diagnosis of microsatellite instability (MSI) or microsatellite stability (MSS).

Methods

We selected 12 tumour samples previously tested for MSI focusing on cases with discrepant results between MLH1, PMS2, MSH2 and MSH6 immunohistochemistry and microsatellite molecular analyses (five cases) or doubtful immunohistochemistry (two cases). Idylla MSI Assay was compared with retrospective immunohistochemistry and molecular results.

Results

Idylla MSI Assay showed an almost perfect concordance with microsatellite analysis results previously obtained (only one case with not fully conclusive analysis due to sample exhaustion). The full molecular analysis took less than 150 min per sample and revealed no mutation in any of the seven microsatellite sequences in five MSS samples and four to six mutated ones in seven MSI-High samples.

Conclusion

At the era when the determination of MSI/MSS status is becoming important for rapid treatment choices, the Idylla MSI Assay consists of a valuable easy-to-perform diagnostic tool that allows, complementary to MLH1, PMS2, MSH2 and MSH6 immunohistochemistry, the diagnosis of MSI/MSS status in a single day.

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.

DNA mismatch repair in cancer

Microsatellite instability (MSI) refers to the hypermutator phenotype secondary to frequent polymorphism in short repetitive DNA sequences and single nucleotide substitution, as consequence of DNA mismatch repair (MMR) deficiency. MSI secondary to germline mutation in DNA MMR proteins is the molecular fingerprint of Lynch syndrome (LS), while epigenetic inactivation of these genes is more commonly found in sporadic MSI tumors. MSI occurs at different frequencies across malignancies, although original methods to assess MSI or MMR deficiency have been developed mostly in LS related cancers. Here we will discuss the current methods to detect MSI/MMR deficiency with a focus of new tools which are emerging as highly sensitive detector for MSI across multiple tumor types. Due to high frequencies of non-synonymous mutations, the presence of frameshift-mutated neoantigens, which can trigger a more robust and long-lasting immune response and strong TIL infiltration with tumor eradication, MSI has emerged as an important predictor of sensitivity for immunotherapy-based strategies, as showed by the recent FDA's first histology agnostic-accelerated approval to immune checkpoint inhibitors for refractory, adult and pediatric, MMR deficient (dMMR) or MSI high (MSI-H) tumors. Moreover, it is known that MSI status may predict cancer response/resistance to certain chemotherapies. Here we will describe the complex interplay between the genetic and clinical-pathological features of MSI/dMMR tumors and the cancer immunotherapy, with a focus on the predictive and prognostic role of MMR status for immune checkpoint inhibitors (ICIs) and providing some suggestions on how to conceive better predictive markers for immunotherapy in the next future.