Prognostic relevance of microsatellite instability in pT3N0M0 colon cancer: a population-based study

Rate of dissemination and prognosis in early and advanced stage colorectal cancer based on microsatellite instability status: systematic review and meta-analysis

INTRODUCTION

For the past two decades, microsatellite instability (MSI) has been reported as a robust clinical biomarker associated with survival advantage attributed to its immunogenicity. However, MSI is also associated with high-risk adverse pathological features (poorly differentiated, mucinous, signet cell, higher grade) and exhibits a double-edged sword phenomenon. We performed a systematic review and meta-analysis to evaluate the rate of dissemination and the prognosis of early and advanced stage colorectal cancer based on MSI status.

METHODS

A systematic literature search of original studies was performed on Ovid searching MEDLINE, Embase, Cochrane Database of Systematic Reviews, American College of Physicians ACP Journal Club, Database of Abstracts of Reviews of Effects DARE, Clinical Trials databases from inception of database to June 2019. Colorectal cancer, microsatellite instability, genomic instability and DNA mismatch repair were used as key words or MeSH terms. The Preferred Reporting Items for Systematic Reviews and Meta-analyses (PRISMA) reporting guideline was followed. Data were pooled using a random-effects model with odds ratio (OR) as the effect size. Statistical analysis was performed using RevMan ver 5.3 Cochrane Collaboration.

RESULTS

From 5288 studies, 136 met the inclusion criteria (n = 92,035; MSI-H 11,746 (13%)). Overall, MSI-H was associated with improved OS (OR, 0.81; 95% CI 0.73-0.90), DFS (OR, 0.73; 95% CI 0.66-0.81) and DSS (OR, 0.69; 95% CI 0.52-0.90). Importantly, MSI-H had a protective effect against dissemination with a significantly lower rate of lymph node and distant metastases. By stage, the protective effect of MSI-H in terms of OS and DFS was observed clearly in stage II and stage III. Survival in stage I CRC was excellent irrespective of MSI status. In stage IV CRC, without immunotherapy, MSI-H was not associated with any survival benefit.

CONCLUSIONS

MSI-H CRC was associated with an overall survival benefit with a lower rate of dissemination. Survival benefit was clearly evident in both stage II and III CRC, but MSI-H was neither a robust prognostic marker in stage I nor stage IV CRC without immunotherapy.

Finding the hot spot: identifying immune sensitive gastrointestinal tumors

Although researchers have been trying to harness the immune system for over 100 years, the advent of immune checkpoint blockers (ICB) marks an era of significant clinical outcomes in various metastatic solid tumors, characterized by complete and durable responses. ICBs are monoclonal antibodies that target either of a pair of transmembrane molecules in tumors or T-cells involved in immune evasion. Currently 2 ICBs targeting the checkpoint program death 1 (PD-1), nivolumab and pembrolizumab, and one cytotoxic lymphocyte antigen-4 (CTLA-4) inhibitor (ipilimumab) are approved in gastrointestinal malignancies. We review herein the current evidence on predictive biomarkers for ICB response in gastrointestinal tumors. A review of literature based on the National Cancer Institute list of FDA-approved drugs for neoplasms and FDA-approved therapies at the FDA website was performed. An initial literature review was based on the American Association for Clinical Research meeting 2019, the American Society of Clinical Oncology meeting 2019 and the European Society of Medical Oncology 2019 proceedings. A systematic search of PubMed was performed involving MeSH browser terms such as biomarkers, immunotherapy, gastrointestinal diseases and neoplasms. When appropriate, American and British terms were used in the search. The most relevant predictor of response to ICBs is microsatellite instability (MSI) and the data is strongest for colorectal cancer. At least 3 prospective trials show evidence of PD-L1 as a predictive biomarker for ICB response in gastroesophageal malignancies. At least one prospective trial has described tumor mutational burden high (TMB-H), independent of MSI, as predictive of response in anal and biliary tract carcinomas. DNA Polymerase Epsilon (POLE) or delta (POL-D) mutations have been implicated in a subset of MSS colorectal cancer with TMB-H but this biomarker requires prospective validation. There is evolving data based on retrospective observations that gene alterations predicting acquired resistance and hyper-progression. Ongoing clinical research is assessing the role of the human microbiome and RNA-editing complex mutations as predictive biomarkers of response to ICBs. MSI has the strongest predictive power among current biomarkers for ICB response in gastrointestinal cancers. Data continue to accumulate from ongoing clinical trials and new biomarkers are emerging from pre-clinical studies, suggesting that drug combinations targeting pathways complimentary to the PD-1/PD-L1 axis inhibition will define a robust field of clinical research.

Clinical Significance and Prognostic Relevance of Microsatellite Instability in Sporadic Colorectal Cancer Patients

Microsatellite instability (MSI) is a marker of the replication error phenotype. It is caused by impaired DNA mismatch repair processes (MMR), resulting in ineffectiveness of the mechanisms responsible for the DNA replication precision and postreplicative DNA repair. MSI underlies the pathogenesis of 10%-20% of colorectal cancer (CRC) cases. The data about the potential value of MMR status as a predictive factor for 5-fluorouracil (FU)-based chemotherapy remain unclear. According to National Comprehensive Cancer Network updated guidelines, MSI testing is recommended for all patients with stage II CRC because patients with MSI-H (high-frequency MSI) tumour may have a good prognosis and obtain no benefit from 5-FU-based adjuvant chemotherapy. The significance of the MSI status as a predictive factor for patients with metastatic disease was not confirmed. The association between the MSI status and the efficacy of the therapy based on anti-programmed death-1 receptor inhibitors requires further studies.

Microsatellite instability and B-type Raf proto-oncogene mutation in colorectal cancer: Clinicopathological characteristics and effects on survival

Prognostic significance of microsatellite instability (MSI) status and B-type Raf proto-oncogene (BRAF) mutation in colorectal cancer is controversial. The aim of this study was to examine the clinical and pathological characteristics associated with microsatellite stability and the effect of MSI and BRAF mutation on the survival of patients with colorectal cancer. The study included 145 colorectal cancer cases. All the patients were examined for DNA mismatch repair (MMR) proteins with an immunohistochemical method. Molecular assessment of MSI was available in a subset of 41 patients. In addition, BRAF mutation analysis was performed in 30 cases. Immunohistochemically, MMR deficiency was present in 28 (19.3%) patients. Female gender (p = 0.001), lesion size ≥5 cm (p = 0.013), Crohn-like response (p = 0.035), and right-sided localization (p < 0.001) were significantly more frequent among MMR-deficient patients. The overall survival was 44.1 ± 5.1 months (95% confidence interval [CI], 33.7-54.4). Multivariate analyses identified only high tumor grade as an independent predictor of poor overall survival: odd ratio, 6.7 (95% CI 2.1-21.7), p = 0.002. In the subset of patients with available BRAF assessment (n = 30), a negative BRAF status was associated with better survival when compared to a positive BRAF status (36.7 ± 2.1 vs. 34.1 ± 7.2 months, p = 0.048). The sensitivity and specificity of the immunohistochemical method in predicting positive MSI status, with the molecular method as a reference, were 85.7% (95% CI: 56.2%-97.5%) and 88.9% (95% CI: 69.7%-97.1%), respectively. BRAF appears to be a significant predictor of a worse outcome in patients with colorectal cancer. Further studies with a large spectrum of clinical and biological variables are warranted.