Immunocheckpoint Inhibitors in Microsatellite-Stable or Proficient Mismatch Repair Metastatic Colorectal Cancer: Are We Entering a New Era?

Colorectal cancer (CRC) is the third most frequent cancer and the second leading cause of cancer-related deaths in Europe. About 5% of metastatic CRC (mCRC) are characterized by high microsatellite instability (MSI) due to a deficient DNA mismatch repair (dMMR), and this condition has been related to a high sensitivity to immunotherapy, in particular to the Immune Checkpoint Inhibitors (ICIs). In fact, in MSI-H or dMMR mCRC, treatment with ICIs induced remarkable response rates and prolonged survival. However, the majority of mCRC cases are mismatch-repair-proficient (pMMR) and microsatellite-stable (MSS), and unfortunately these conditions involve resistance to ICIs. This review aims to provide an overview of the strategies implemented to overcome ICI resistance and/or define subgroups of patients with MSS or dMMR mCRC who may benefit from immunotherapy.

Refractory microsatellite stable metastatic colorectal cancer with ERBB2/ERBB3 mutation may be preferred population for regorafenib plus PD-1 inhibitor therapy: a real-world study

Background

Microsatellite stable (MSS) colorectal cancer (CRC) has been referred to as the "cold tumor" because of almost no response to anti-programmed death-1 (PD-1) antibody. A recent REGONIVO trial showed that regorafenib plus nivolumab had an encouraging efficacy in MSS metastatic CRC (mCRC). However, only a small subset of patients may benefit from the combination therapy. We aim to evaluate the efficacy and safety data of immune checkpoint inhibitors combined with regorafenib in refractory MSS mCRC and to discover biomarkers that can effectively stratify the beneficial patient population.

Methods

We retrospectively analyzed patients with MSS mCRC who received regorafenib combined with anti-PD-1 antibody therapy. The objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS), and status of gene mutation were reviewed and evaluated.

Results

Twenty-one patients received combination treatment. At a median treatment duration of 4 months, one patient achieved complete response, three patients achieved partial response, and two patients achieved stable disease as the best response. The ORR and DCR were 19% and 28.5% in the overall population, respectively. The median PFS was 4 months, and the median OS was 25 months. Only erbb2 receptor tyrosine kinase 2/erbb3 receptor tyrosine kinase 3 (ERBB2/ERBB3) mutation status was confirmed to be a potential predictive factor for effective treatment. In patients with ERBB2/ERBB3 mutation, ORR, DCR, and PFS exhibited significant improvements in comparison with that in wild-type patients. Grade 3 or higher treatment-related adverse events occurred in three patients (14.3%).

Conclusions

Regorafenib in combination with PD-1 inhibitor provides a feasible treatment regimen for refractory MSS mCRC with tolerated toxicity. Patients with ERBB2/ERBB3 mutation may be the preferred population for this combination regimen.

Light on life: immunoscore immune-checkpoint, a predictor of immunotherapy response

In the last decade, a plethora of immunotherapeutic strategies have been designed to modulate the tumor immune microenvironment. In particular, immune checkpoint (IC) blockade therapies present the most promising advances made in cancer treatment in recent years. In non-small cell lung cancer (NSCLC), biomarkers predicting response to IC treatments are currently lacking. We have recently identified Immunoscore-IC, a powerful biomarker that predicts the efficiency of immune-checkpoint inhibitors (ICIs) in NSCLC patients. Immunoscore-IC is an in vitro diagnostic assay that quantifies densities of PD-L1+, CD8+ cells, and distances between CD8+ and PD-L1+ cells in the tumor microenvironment. Immunoscore-IC can classify responder vs non-responder NSCLC patients for ICIs therapy and is revealed as a promising predictive marker of response to anti-PD-1/PD-L1 immunotherapy in these patients. Immunoscore-IC has also shown a significant predictive value, superior to the currently used PD-L1 marker. In colorectal cancer (CRC), the addition of atezolizumab to first-line FOLFOXIRI plus bevacizumab improved progression-free survival (PFS) in patients with previously untreated metastatic CRC. In the AtezoTRIBE trial, Immunoscore-IC emerged as the first biomarker with robust predictive value in stratifying pMMR metastatic CRC patients who critically benefit from checkpoint inhibitors. Thus, Immunoscore-IC could be a universal biomarker to predict response to PD-1/PD-L1 checkpoint inhibitor immunotherapy across multiple cancer indications. Therefore, cancer patient stratification (by Immunoscore-IC), based on the presence of T lymphocytes and PD-L1 potentially provides support for clinicians to guide them through combination cancer treatment decisions.

Update on Emerging Therapies for Advanced Colorectal Cancer

Colorectal cancer (CRC) is the third most common malignancy worldwide. It is projected to increase by 3.2 million new cases and account for 1.6 million deaths by 2040. Mortality is largely due to limited treatment options for patients who present with advanced disease. Thus, the development of effective and tolerable therapies is crucial. Chemotherapy has been the backbone of systemic treatment of advanced CRC, but utility has been limited because of invariable resistance to therapy, narrow mechanisms of action, and unfavorable toxicity profile. Tumors that are mismatch repair-deficient have demonstrated remarkable response to immune checkpoint inhibitor therapy. However, most CRC tumors are mismatch repair-proficient and represent an unmet medical need. Although ERBB2 amplification occurs only in a few cases, it is associated with left-sided tumors and a higher incidence of brain metastasis. Numerous combinations of HER2 inhibitors have demonstrated efficacy, and antibody-drug conjugates against HER2 represent innovative strategies in this area. The KRAS protein has been classically considered undruggable. Fortunately, new agents targeting KRAS G12C mutation represent a paradigm shift in the management of affected patients and could lead the advancement in drug development for the more common KRAS mutations. Furthermore, aberrant DNA damage response is present in 15%-20% of CRCs, and emerging innovative combinations with poly (ADP-ribose) polymerase (PARP) inhibitors could improve the current therapeutic landscape. Multiple novel biomarker-driven approaches in the management of patients with advanced CRC tumors are reviewed in this article.

Advances in immune checkpoint inhibitor combination strategies for microsatellite stable colorectal cancer

Immune checkpoint inhibitors have reshaped the prognostic of several tumor types, including metastatic colorectal tumors with microsatellite instability (MSI). However, 90-95% of metastatic colorectal tumors are microsatellite stable (MSS) in which immunotherapy has failed to demonstrate meaningful clinical results. MSS colorectal tumors are considered immune-cold tumors. Several factors have been proposed to account for this lack of response to immune checkpoint blockade including low levels of tumor infiltrating lymphocytes, low tumor mutational burden, a high rate of WNT/β-catenin pathway mutations, and liver metastases which have been associated with immunosuppression. However, studies with novel combinations based on immune checkpoint inhibitors are showing promising activity in MSS colorectal cancer. Here, we review the underlying biological facts that preclude immunotherapy activity, and detail the different immune checkpoint inhibitor combinations evaluated, along with novel immune-based therapies, to overcome innate mechanisms of resistance in MSS colorectal cancer.

Current Landscape and Potential Challenges of Immune Checkpoint Inhibitors in Microsatellite Stable Metastatic Colorectal Carcinoma

Colorectal cancer (CRC) is the third most frequent cancer and the second most common cause of cancer-related death in Europe. High microsatellite instability (MSI-H) due to a deficient DNA mismatch repair (dMMR) system can be found in 5% of metastatic CRC (mCRC) and has been established as a biomarker of response to immunotherapy in these tumors. Therefore, immune checkpoint inhibitors (ICIs) in mCRC with these characteristics were evaluated with results showing remarkable response rates and durations of response. The majority of mCRC cases have high levels of DNA mismatch repair proteins (pMMR) with consequent microsatellite stability or low instability (MSS or MSI-low), associated with an inherent resistance to ICIs. This review aims to provide a comprehensive analysis of the possible approaches to overcome the mechanisms of resistance and evaluates potential biomarkers to establish the role of ICIs in pMMR/MSS/MSI-L (MSS) mCRC.

Acute inflammatory reaction during anti-angiogenesis therapy combined with immunotherapy as a possible indicator of the therapeutic effect: Three case reports and literature review

The posterior line treatment of unresectable advanced or metastatic gastrointestinal (GI) tumors has always been a challenging point. In particular, for patients with microsatellite stable (MSS)/mismatch repair proficient (pMMR) 0GI tumors, the difficulty of treatment is exacerbated due to their insensitivity to immune drugs. Accordingly, finding a new comprehensive therapy to improve the treatment effect is urgent. In this study, we report the treatment histories of three patients with MSS/pMMR GI tumors who achieved satisfactory effects by using a comprehensive treatment regimen of apatinib combined with camrelizumab and TAS-102 after the failure of first- or second-line regimens. The specific contents of the treatment plan were as follows: apatinib (500 mg/d) was administered orally for 10 days, followed by camrelizumab (200 mg, ivgtt, day 1, 14 days/cycle) and TAS-102 (20 mg, oral, days 1-21, 28 days/cycle). Apatinib (500 mg/d) was maintained during treatment. Subsequently, we discuss the possible mechanism of this combination and review the relevant literature, and introduce clinical trials on anti-angiogenesis therapy combined with immunotherapy.

Low-dose immunogenic chemotherapeutics promotes immune checkpoint blockade in microsatellite stability colon cancer

More than 85% of colorectal cancer (CRC) patients, who are with microsatellite stability (MSS), are resistant to immune checkpoint blockade (ICB) treatment. To overcome this resistance, combination therapy with chemotherapy is the most common choice. However, many CRC patients do not benefit more from combination therapy than chemotherapy alone. We hypothesize that severe immunosuppression, caused by chemotherapy administered at the maximum tolerated dose, antagonizes the ICB treatment. In this study, we found that low-dose oxaliplatin (OX), an immunogenic cell death (ICD)-induced drug, increased the antitumor response of TIGIT blockade against CT26 tumor, which is regarded as a MSS tumor. Combined treatment with OX and TIGIT blockade fostered CD8+ T-cell infiltration into tumors and delayed tumor progression. Importantly, only low-dose immunogenic chemotherapeutics successfully sensitized CT26 tumors to TIGIT blockade. In contrast, full-dose OX induces severe immunosuppression and impaired the efficacy of combination therapy. Further, we also found that lack of synergy between nonimmunogenic chemotherapeutics and TIGIT blockade. Consequently, this study suggests that the strategies of combination treatment of chemotherapy and ICB should be re-evaluated. The chemotherapeutics should be chosen for the potential to ICD and the dosage and regimen should be also optimized.

Immune Checkpoint Inhibitors for Gastrointestinal Malignancies: An Update

Simple Summary

Immune checkpoint inhibitors are a class of anti-cancer therapy that work by harnessing the body’s immune system to promote cancer cell death. These drugs have become standard of care for many types of cancer, including melanoma and lung cancer, after clinical trials showed they work better than traditional chemotherapy. The role of immune checkpoint inhibitors is still evolving in the treatment of cancers of the gastrointestinal tract. This article examines the literature to support the use of immune checkpoint inhibitors to treat cancers of each part of the gastrointestinal system.

Abstract

Gastrointestinal (GI) malignancies are a heterogenous group of cancers with varying epidemiology, histology, disease course, prognosis and treatment options. Immune checkpoint inhibitors (ICIs) have changed the landscape of modern cancer treatment, though they have demonstrated survival benefit in other solid tumors more readily than in GI malignancies. This review article presents an overview of the landscape of ICI use in GI malignancies and highlights recent updates in this rapidly evolving field.

Mismatch Repair-Deficient Colorectal Cancer: Building on Checkpoint Blockade

Colorectal cancer (CRC) with deficient DNA mismatch repair (dMMR) is characterized by hypermutation leading to abundant neoantigens that activate an antitumor immune response in the tumor microenvironment. Immune checkpoint inhibitors (ICIs) have transformed the treatment of this subset of CRC and other solid tumors with dMMR, by producing frequent and durable responses that extend patient survival. Recently, the anti-programmed death-1 (PD-1) antibody pembrolizumab was shown to produce significantly longer progression-free survival with fewer adverse events compared with chemotherapy as first-line treatment of metastatic CRC (mCRC) with dMMR. Accordingly, single-agent pembrolizumab represents a new standard of care for dMMR mCRCs including patients with Lynch syndrome and the more common sporadic cases. Furthermore, data indicate that the combination of PD-1 and cytotoxic T-cell lymphocyte-4 inhibitors was more effective than single-agent PD-1 inhibition in patients with dMMR mCRCs, suggesting nonredundant mechanisms of action. Although the benefit of ICIs is currently limited to metastatic disease, studies evaluating ICIs as neoadjuvant and adjuvant therapy in earlier-stage dMMR CRC are ongoing. Despite success of ICIs in the treatment of metastatic dMMR cancers, an appreciable proportion of these tumors demonstrate intrinsic or acquired resistance, and biomarkers to identify these patients are needed. Advances in the understanding of immunotherapy resistance mechanisms hold promise for both biomarker identification and development of novel strategies to circumvent treatment resistance. In this review, we present a comprehensive overview of the evidence for the role of immunotherapy in the treatment of dMMR CRC, discuss resistance mechanisms, and outline potential strategies to circumvent primary and secondary resistance with the goal of broadening the benefit of ICIs.

Individualized, heterologous chimpanzee adenovirus and self-amplifying mRNA neoantigen vaccine for advanced metastatic solid tumors: phase 1 trial interim results

Checkpoint inhibitor (CPI) therapies provide limited benefit to patients with tumors of low immune reactivity. T cell-inducing vaccines hold promise to exert long-lasting disease control in combination with CPI therapy. Safety, tolerability and recommended phase 2 dose (RP2D) of an individualized, heterologous chimpanzee adenovirus (ChAd68) and self-amplifying mRNA (samRNA)-based neoantigen vaccine in combination with nivolumab and ipilimumab were assessed as primary endpoints in an ongoing phase 1/2 study in patients with advanced metastatic solid tumors (NCT03639714). The individualized vaccine regimen was safe and well tolerated, with no dose-limiting toxicities. Treatment-related adverse events (TRAEs) >10% included pyrexia, fatigue, musculoskeletal and injection site pain and diarrhea. Serious TRAEs included one count each of pyrexia, duodenitis, increased transaminases and hyperthyroidism. The RP2D was 10¹² viral particles (VP) ChAd68 and 30 µg samRNA. Secondary endpoints included immunogenicity, feasibility of manufacturing and overall survival (OS). Vaccine manufacturing was feasible, with vaccination inducing long-lasting neoantigen-specific CD8 T cell responses. Several patients with microsatellite-stable colorectal cancer (MSS-CRC) had improved OS. Exploratory biomarker analyses showed decreased circulating tumor DNA (ctDNA) in patients with prolonged OS. Although small study size limits statistical and translational analyses, the increased OS observed in MSS-CRC warrants further exploration in larger randomized studies.

Prognostic and predictive molecular biomarkers in advanced colorectal cancer

The revolution of precision medicine has produced unprecedented seismic shifts in the treatment paradigm of advanced cancers. Among the major killers, colorectal cancer (CRC) is far behind the others. In fact, the great successes obtained in breast, NSCLC, melanoma, and genitourinary tract tumors have been observed only in fewer than 5 % metastatic colorectal cancer (mCRC): those with the mismatch repair deficiency (dMMR), a well-known predictive factor for to the outstanding efficacy of checkpoint inhibitors (CPI). The treatment of the remaining vast majority mCRC patients is still based upon only two molecular determinants: the RAS and BRAF mutational status. New promising biomarkers include HER2, tumor mutational burden (TMB) for its possible implications on CPI efficacy, and the extremely rare NTRK fusions. The Consensus Molecular Subtypes classification (CMS) is a good example of the efforts to combine different molecular features of this disease, although its relevance in clinical practice is still under investigation. In this Review, we focus on all these prognostic and predictive biomarkers, analyzing data from the most important clinical trials of the last years. We also try to rank them according to their prognostic and predictive power.

Clinical management of metastatic colorectal cancer in the era of precision medicine

Colorectal cancer (CRC) represents approximately 10% of all cancers and is the second most common cause of cancer deaths. Initial clinical presentation as metastatic CRC (mCRC) occurs in approximately 20% of patients. Moreover, up to 50% of patients with localized disease eventually develop metastases. Appropriate clinical management of these patients is still a challenging medical issue. Major efforts have been made to unveil the molecular landscape of mCRC. This has resulted in the identification of several druggable tumor molecular targets with the aim of developing personalized treatments for each patient. This review summarizes the improvements in the clinical management of patients with mCRC in the emerging era of precision medicine. In fact, molecular stratification, on which the current treatment algorithm for mCRC is based, although it does not completely represent the complexity of this disease, has been the first significant step toward clinically informative genetic profiling for implementing more effective therapeutic approaches. This has resulted in a clinically relevant increase in mCRC disease control and patient survival. The next steps in the clinical management of mCRC will be to integrate the comprehensive knowledge of tumor gene alterations, of tumor and microenvironment gene and protein expression profiling, of host immune competence as well as the application of the resulting dynamic changes to a precision medicine-based continuum of care for each patient. This approach could result in the identification of individual prognostic and predictive parameters, which could help the clinician in choosing the most appropriate therapeutic program(s) throughout the entire disease journey for each patient with mCRC. CA Cancer J Clin. 2022;72:000-000.

Comparative Safety, Efficacy and Survival Outcome of Anti-PD-1 Immunotherapy in Colorectal Cancer Patients With vs Without Hepatitis B Virus Infection: A Multicenter Cohort Study

INTRODUCTION

Antiprogrammed cell death protein-1 (PD-1) immunotherapy has substantially broadened in scope for the treatment of colorectal cancer (CRC). However, comparative safety, efficacy and survival outcome of anti-PD-1 therapy in CRC patients with and without hepatitis B virus (HBV) infection remain unclear.

METHODS

This multicenter, retrospective cohort study included 180 advanced-stage CRC patients with available serological markers for HBV infection treated with anti-PD-1 therapy at the Sixth Affiliated Hospital, Sun Yat-sen University and Sun Yat-sen University Cancer Center between December 2016 and December 2019. A propensity score-matched analysis was performed to compare the safety, efficacy, and survival outcome between HBV and non-HBV groups.

RESULTS

The incidences of deficient mismatch repair and metastatic disease were significantly different between HBV and non-HBV groups (both P < 0.05). After propensity score-matched analysis, any grade immune-related adverse events and grade ≥ 3 immune-related adverse events were 47% vs 38% (P = 0.25) and 5% vs 6% (P = 1.0) between HBV and non-HBV groups, respectively. The overall response rate was 39% with 17 complete responses and 13 partial responses for the HBV infection cohort and 39% with 11 complete responses and 19 partial responses for the non-HBV infection cohort (P = 1.0). Two-year progression-free survival rates were 38% vs 40% (P = 0.596) and 2-year overall survival rates were 55% vs 63% (P = 0.401) for HBV vs non-HBV infection cohorts.

DISCUSSION

The incidences of toxicity, efficacy and survival outcome were similar between patients with HBV infection and non-HBV patients receiving anti-PD-1 therapy, which supports to include CRC patients with HBV in clinical trials of anti-PD-1 therapy.

Regorafenib combined with programmed cell death-1 inhibitor against refractory colorectal cancer and the platelet-to-lymphocyte ratio’s prediction on effectiveness

BACKGROUND

The effectiveness of regorafenib plus programmed cell death-1 (PD-1) inhibitor in treating microsatellite stable (MSS) metastatic colorectal cancer (mCRC) remains controversial.

AIM

To investigate the benefits of regorafenib combined with PD-1 inhibitor in treating MSS mCRC and explore indicators predicting response.

METHODS

This retrospective study included a total of 30 patients with microsatellite stable metastatic colorectal cancer treated with regorafenib combined with programmed cell death-1 inhibitor at Henan Provincial People’s Hospital between December 2018 and December 2020. During a 4-wk treatment cycle, regorafenib was performed for 3 continuous weeks. PD-1 inhibitor was intravenously injected starting on the first day of the oral intake of regorafenib. We reviewed tumor response, progression-free survival (PFS), overall survival, and treatment-related adverse events (TRAEs) and evaluated association between platelet-to-lymphocyte ratio (PLR) and outcomes in this retrospective study.

RESULTS

Stable disease and progressive disease were found in 18 (60.0%) and 12 (40.0%) patients, respectively. The disease control rate was 60.0%. The median follow-up time was 12.0 mo, and median PFS was 3.4 mo [95% confidence interval (CI): 2.2-4.6 mo]. Of the 12 patients with progressive disease, 10 (83.3%) had liver metastasis before starting the combined treatment. Among the 18 patients with SD, 10 (55.6%) did not have liver metastases. One patient without liver metastases at baseline was found with a substantially prolonged PFS of 11.2 mo. The liver metastasis, the choice of programmed cell death-1 inhibitor other than nivolumab or pembrolizumab and previous exposure to regorafenib was’t associated with treatment outcome. The median PFS in the low-PLR group was 4.2 mo (95%CI: 3.5-4.9 mo), compared with 2.8 mo (95%CI: 1.4-4.2 mo) in the high-PLR group (P = 0.005). The major TRAEs included hand-foot syndrome (33.3%), hypertension (23.3%), malaise (20.0%), and gastrointestinal reaction (16.7%). The incidence of grade 3 TRAEs was 13.3% (4/30), which comprised abnormal capillary proliferation (n = 1), transaminase elevation (n = 1), and hand-foot syndrome (n = 2). No grade 4 or higher toxicity was observed.

CONCLUSION

Regorafenib combined with PD-1 inhibitor could lead to a longer PFS in some patients with MSS mCRC. The PLR might be a prediction of the patient response to this therapy.

Does the Microbiota Composition Influence the Efficacy of Colorectal Cancer Immunotherapy?

Colorectal cancer (CRC) is the second most common malignancy globally, and many people with CRC suffer the fate of death. Due to the importance of CRC and its negative impact on communities, treatment strategies to control it or increase patient survival are being studied. Traditional therapies, including surgery and chemotherapy, have treated CRC patients. However, with the advancement of science, we are witnessing the emergence of novel therapeutic approaches such as immunotherapy for CRC treatment, which have had relatively satisfactory clinical outcomes. Evidence shows that gastrointestinal (GI) microbiota, including various bacterial species, viruses, and fungi, can affect various biological events, regulate the immune system, and even treat diseases like human malignancies. CRC has recently shown that the gut microorganism pattern can alter both antitumor and pro-tumor responses, as well as cancer immunotherapy. Of course, this is also true of traditional therapies because it has been revealed that gut microbiota can also reduce the side effects of chemotherapy. Therefore, this review summarized the effects of gut microbiota on CRC immunotherapy.

PD-1/PD-L1 blockade, a novel strategy for targeting metastatic colorectal cancer: A systematic review and meta-analysis of randomized trials

Currently, standard treatment of patients with metastatic colorectal cancer (mCRC) comprises chemotherapy (CT) and/or biological therapy (BT) and/or best supportive care (BSC). The present study performed a meta-analysis on five phase II-III randomized clinical trials, which compared CT/BT/BSC as the control arm with the immune checkpoint inhibitors (ICIs) anti-programmed cell death protein 1 (PD-1) or its ligand (PD-L1) alone or in combination with cytotoxic T lymphocyte antigen 4 or mitogen activated protein kinase kinase inhibitors as the experimental arm, to evaluate whether a standard approach could be overcome using the novel target therapy strategy. Pooled hazard ratio (HR) for progression-free survival was 0.95 in favor of the experimental arm [95% confidence interval (CI), 0.74-1.22; P=0.68]. Heterogeneity was significant: Cochran's Q, 21.0; P=0.0082; I2 index, 76%. Pooled HR for overall survival was 0.88 in favor of the experimental arm (95% CI, 0.75-1.02; P=0.08). Heterogeneity was not significant (Cochran's Q, 6.0; P=0.31; I2 index, 16%). The present meta-analysis demonstrated a trend toward the improvement of survival by PD-1/PD-L1 blockade in mCRC. Further homogeneous studies are necessary to strengthen these results, beyond the known benefits of ICIs in deficient mismatch repair/high microsatellite instability tumors.

Clinical significance of molecular subtypes of gastrointestinal tract adenocarcinoma

Adenocarcinomas of the gastrointestinal tract (esophagus, stomach, and colon) represent a heterogeneous group of diseases with distinct etiology, clinical features, treatment approaches, and prognosis. Studies are ongoing to isolate molecular genetic subtypes, perform complete biological characterization of the tumor, determine prognostic groups, and find predictive markers to the effectiveness of therapy. Separate molecular genetic classifications were created for esophageal adenocarcinoma [The Cancer Genome Atlas (TCGA)], stomach cancer (TCGA, Asian Cancer Research Group), and colon cancer (Colorectal Cancer Subtyping Consortium). In 2018, isolation of TCGA molecular genetic subtypes for adenocarcinomas of the gastrointestinal tract (esophagus, stomach, and colon) highlighted the need for further studies and clinical validation of subtyping of gastrointestinal adenocarcinomas. However, this approach has limitations. The aim of our work was to critically analyze integration of molecular genetic subtyping of gastrointestinal adenocarcinomas in clinical practice.

The Current and Evolving Role of Immunotherapy in Metastatic Colorectal Cancer

Immunotherapy can be considered a therapeutic revolution in oncology, with great impact on many tumor types, such as melanoma and non-small cell lung cancer. However, in metastatic colorectal cancer, the benefits in terms of prolonged tumor control and high response rate are limited to the rare subgroup of tumors with high mutation burden - mostly tumors that harbor microsatellite instability (MSI) or a deficient mismatch repair system (dMMR), or tumor microsatellite stability and damaging mutations in the exonuclease domains of POLE or POLD. The KEYNOTE-028 uncontrolled phase II trial demonstrated an impressive antitumor activity of pembrolizumab in patients with treatment-refractory Lynch-associated tumors, including colorectal cancer. Nivolumab with or without ipilimumab confirmed the efficacy of immune checkpoint inhibitors in patients with previously treated dMMR / MSI metastatic colorectal cancer. The recent KEYNOTE-177 phase III trial demonstrated that pembrolizumab significantly reduced the relative risk of disease progression or death and improved progression-free survival in patients with treatment-naive dMMR / MSI metastatic colorectal cancer in comparison with first-line chemotherapy with or without biologics. Unfortunately, current pharmacological strategies with immunotherapy have not been successful for most patients with microsatellite stable metastatic colorectal cancer. In this review we critically appraise the applicability of immune checkpoint inhibitors in dMMR/MSI metastatic colorectal cancer. We also discuss the recent negative trials of immunotherapy combinations in microsatellite stable tumors and the more mature immunotherapy ongoing studies in the field of advanced colorectal cancer.

Immune Checkpoint Inhibitors in Mismatch Repair Proficient/Microsatellite Stable Metastatic Colorectal Cancer Patients: Insights from the AtezoTRIBE and MAYA Trials

Simple Summary

Immune-checkpoint inhibitors (ICI) show modest activity and efficacy in microsatellite stable (MSS) metastatic colorectal cancer (mCRC) patients harbouring a proficient mismatch repair system (pMMR). Recently, two phase 2 trials -AtezoTRIBE and MAYA- have challenged this dogma through the administration of an intense first-line chemotherapy backbone consisting of FOLFOXIRI/bevacizumab in patients unselected for their microsatellite status, and immune priming with temozolomide in chemorefractory pMMR/MSS patients with silencing of O6-methylguanine-DNA methyltransferase (MGMT), respectively, reporting promising results. We here present the founding biological rationale of these two studies and their main findings. At the same time, we stress their strengths and drawbacks and open questions still to be address in future clinical investigations.

Abstract

In metastatic colorectal cancer (mCRC), remarkable advances have been achieved with immune checkpoint inhibitors (ICIs) targeting PD-1/PD-L1 and CTLA-4, only in a small subset of tumours (4–5%), harbouring a deficient mismatch repair system (dMMR)/microsatellite instability–high (MSI-H) or mutations in the catalytic subunit of polymerase epsilon (POLE). Within this framework, several combination strategies have been investigated to sensitize proficient mismatch repair (pMMR)/microsatellite stable (MSS) mCRC to ICIs, with disappointing results so far. However, at the last ESMO meeting, two phase II trials AtezoTRIBE and MAYA provided promising results in this field. In the comparative AtezoTRIBE trial, the addition of atezolizumab to FOLFOXIRI (5-fluoruracil, oxaliplatin and irinotecan) and bevacizumab led to a significant advantage in terms of progression free survival (PFS) in a population of untreated mCRC patients, not selected according to MMR/MSI status. In the single-arm MAYA trial, immune priming with temozolomide in pMMR/MSS chemo-resistant mCRC patients with silencing of O6-methylguanine-DNA methyltransferase (MGMT) allowed reporting signals of sensitivity to the subsequent therapy with nivolumab and a low dose of ipilimumab in some patients. Here, we discuss the rationale, results, criticisms and research perspectives opened by these two studies.

Combined Treatment with Immunotherapy-Based Strategies for MSS Metastatic Colorectal Cancer

In recent years, deepening knowledge of the complex interactions between the immune system and cancer cells has led to the advent of effective immunotherapies that have revolutionized the therapeutic paradigm of several cancer types. However, colorectal cancer (CRC) is one of the tumor types in which immunotherapy has proven less effective. While there is solid clinical evidence for the therapeutic role of immune checkpoint inhibitors in mismatch repair-deficient (dMMR) and in highly microsatellite instable (MSI-H) metastatic CRC (mCRC), blockade of CTLA-4 or PD-L1/PD-1 as monotherapy has not conferred any major clinical benefit to patients with MMR-proficient (pMMR) or microsatellite stable (MSS) mCRC, reflecting 95% of the CRC population. There thus remains a high unmet medical need for the development of novel immunotherapy approaches for the vast majority of patients with pMMR or MSS/MSI-low (MSI-L) mCRC. Defining the molecular mechanisms for immunogenicity in mCRC and mediating immune resistance in MSS mCRC is needed to develop predictive biomarkers and effective therapeutic combination strategies. Here we review available clinical data from combinatorial therapeutic approaches using immunotherapy-based strategies for MSS mCRC.

Preliminary Efficacy and Safety of Camrelizumab in Combination With XELOX Plus Bevacizumab or Regorafenib in Patients With Metastatic Colorectal Cancer: A Retrospective Study

Background

For a majority of patients with metastatic colorectal cancer (mCRC) with MS stable (MSS) or mismatch repair proficient (pMMR), the role of immunotherapy is undetermined. This study investigated the efficacy and safety of camrelizumab when added to XELOX chemotherapy plus bevacizumab or regorafenib as first-line therapy for mCRC.

Materials and Methods

Medical records of mCRC patients who received camrelizumab and XELOX plus bevacizumab or regorafenib at the First Hospital of Quanzhou Affiliated to Fujian Medical University between June 1, 2019, and April 30, 2021, were retrospectively collected. The objective response rate (ORR), disease control rate (DCR), progression-free survival (PFS), overall survival (OS), and side effects of the drug were recorded and reviewed.

Results

Twenty-five eligible patients received combination therapy, including bevacizumab in 19 patients and regorafenib in 6. Twenty-one patients had pMMR/MSS and one MSI-H. Of the 25 patients who could be evaluated for efficacy, 18 (72%) achieved PR, 6 (24%) achieved SD, and 1 (4%) achieved PD. The ORR and DCR were 72% (18/25) and 96% (24/25), respectively. The median progression-free survival (PFS) was 11.2 months (95% CI 8.9–13.9), and OS had not yet been reached. The combination regimen of regorafenib in six (24%) patients was unassociated with treatment outcomes. Most AEs were either grade 1 or 2, and treatment-related grade 3 toxicities were observed in 8/25 (32%) patients.

Conclusion

Camrelizumab combined with XELOX plus bevacizumab or regorafenib was feasible, producing high rates of responses as first-line therapy in unselected Chinese patients with MSS mCRC. The toxicities were generally tolerable and manageable. Prospective randomized trials with large sample sizes are needed to evaluate these findings.

Towards exertion of immunotherapeutics in the treatment of colorectal cancer; adverse sides, challenges, and future directions

Immunotherapy has growingly been prosperous as a promising therapeutic option for several kinds of solid tumors, such as colorectal cancer (CRC), subsequent to initial successful outcomes in the treatment of melanoma. The use of immunotherapy, like nivolumab and pembrolizumab (which are monoclonal antibodies against programmed cell death 1) has shown prosperous outcomes in a group of CRC patients who represent mismatch-repair-deficient and microsatellite instability-high (dMMR-MSI-H). However, a successful outcome of treatment by immune checkpoint inhibitors (ICIs) has not been observed in all of the metastatic CRC patients with dMMR-MSI-H tumors. ICIs are able to block the co-inhibitory signaling transduced in T cells, resulting in increased cytotoxic activity of T cells and efficient killing of tumor cells. In spite of availability of diverse immunotherapeutics in treatment of advanced CRC, a poor survival rate of such approaches has been reported along with challenges in the clinical practice. It is necessary to identify novel biomarkers and molecular signatures to approximate the outcome of ICI therapy in the metastatic CRC patients with dMMR-MSI-H tumors. Here we tried to clarify the current line of evidence regarding immunotherapeutics in the treatment of CRC, and discuss the challenges and hurdles in the management of these patients.

Proteasome inhibitors restore the STAT1 pathway and enhance the expression of MHC class I on human colon cancer cells

BACKGROUND

A new strategy, particularly a novel combination, for immunotherapy in microsatellite stable metastatic colorectal cancer (mCRC) treatment needs to be formulated. Studies on the interferon-γ (IFN-γ)/ Janus kinase (JAK)/ signal transducer and activator of transcription (STAT)1 pathway provide new directions in this regard.

METHODS

Our study applies three colon cancer cell lines, including microsatellite stable (MSS) cell lines, which are SW480 and SW620, and microsatellite instability-high (MSI-H) cell line, which is DLD-1. We compared the expressions of immune surface markers on colon cancer cells in response to IFN-γ. We elucidated these mechanisms, which involved the upregulation of immune surface markers. Furthermore, we examined real-world clinical samples using the PerkinElmer Opal multiplex system and NanoString analysis.

RESULTS

We established that the baseline expression of major histocompatibility complex (MHC) class I alleles and programmed death-ligand 1 (PD-L1) were generally low in cell line models. The immune surface markers were significantly increased after IFN-γ stimulation on SW480 but were notably unresponsive on the SW620 cell line. We discovered that STAT1 and phosphorylated STAT1 (pSTAT1) were downregulated in the SW620 cell line. We verified that the STAT1/pSTAT1 could be restored through the application of proteasome inhibitors, especially bortezomib. The expression of MHC class I as downstream signals of STAT1 was also up-regulated by proteasome inhibitors. The similar results were reproduced in DLD-1 cell line, which was also initially unresponsive to IFN-γ. In real-world samples of patients with mCRC, we found that higher STAT1 expression in tumor cells was strongly indicative of a highly immunogenic microenvironment, with significantly higher expression levels of MHC class I and PD-L1, not only on tumor cells but also on non-tumor cells. Furthermore, tumor infiltrating lymphocytes (TILs) were increased in the positive-STAT1 group. Through NanoString analysis, we confirmed that the mRNA expressions of IFN-γ, human leukocyte antigen (HLA)-A, HLA-E, and HLA-G were also significantly higher in the positive-STAT1 group than those in the negative-STAT1 group.

CONCLUSION

Our study provides a novel rationale for the addition of bortezomib, a proteasome inhibitor, into new immunotherapy combinations.

Clinical Application of Adaptive Immune Therapy in MSS Colorectal Cancer Patients

Colorectal cancer (CRC) is one of the most common cancers worldwide. However, the treatment outcomes of immunotherapy in microsatellite-stable (MSS) CRC remain unsatisfactory. As the majority of CRC cases display a molecular MSS/mismatch repair-proficient (pMMR) profile, it is particularly meaningful to explore the clinical applications of adaptive immune therapy in MSS CRC patients. In this review, we summarized the therapeutic approaches of adoptive immune therapies, including cytokines, therapeutic cancer vaccines, adoptive T-cell therapy, and immune checkpoint inhibitors, in the treatment of MSS CRCs.

Pembrolizumab with Capox Bevacizumab in patients with microsatellite stable metastatic colorectal cancer and a high immune infiltrate: The FFCD 1703-POCHI trial

Pembrolizumab, a PD1 immune checkpoint inhibitor (ICI), was recently reported to be very effective in patients with microsatellite instable/deficient mismatch repair metastatic colorectal cancer (MSI/dMMR mCRC), unlike patients with microsatellite stable/proficient MMR (MSS/pMMR) mCRC, in whom ICIs are generally ineffective. However, about 15% of MSS/pMMR CRCs are highly infiltrated by tumour infiltrating lymphocytes. In addition, both oxaliplatin and bevacizumab have been shown to have immunomodulatory properties that may increase the efficacy of an ICI. We formulated the hypothesis that patients with MSS/pMMR mCRC with a high immune infiltrate can be sensitive to ICI plus oxalipatin and bevacizumab-based chemotherapy. POCHI is a multicenter, open-label, single-arm phase II trial to evaluate efficacy of Pembrolizumab with Capox Bevacizumab as first-line treatment of MSS/pMMR mCRC with a high immune infiltrate for which we plan to enrol 55 patients. Primary endpoint is progression-free survival (PFS) at 10 months, which is expected greater than 50%, but a 70% rate is hoped for. Main secondary objectives are overall survival, secondary resection rate and depth of response. Patients must have been resected of their primary tumour so as to evaluate two different immune scores (Immunoscore® and TuLIS) and are eligible if one score is "high". The first patient was included on April 20, 2021.

Regorafenib plus toripalimab in patients with metastatic colorectal cancer: a phase Ib/II clinical trial and gut microbiome analysis

This is a phase Ib/II study of regorafenib plus toripalimab for colorectal cancer. The objective response rate (ORR) is 15.2% and the disease control rate is 36.4% in evaluable patients with recommended phase II dose (80 mg regorafenib plus toripalimab). The median progression-free survival (PFS) and the median overall survival are 2.1 months and 15.5 months, respectively. Patients with liver metastases have lower ORR than those without (8.7% versus 30.0%). All patients (3/3) with lung-only metastasis respond, whereas no patients (0/4) with liver-only metastasis respond. 94.9% and 38.5% of patients have grade 1 and grade 3 treatment-related adverse events, respectively. Gut microbiome analysis of the baseline fecal samples shows significantly increased relative abundance and positive detection rate of Fusobacterium in non-responders than responders. Patients with high-abundance Fusobacterium have shorter PFS than those with low abundance (median PFS = 2.0 versus 5.2 months; p = 0.002).

Treatment Efficacy of Immune Checkpoint Inhibitors for Patients with Advanced or Metastatic Colorectal Cancer: A Systematic Review and Meta-Analysis

The treatment efficacy of immune checkpoint inhibitors (ICIs) in colorectal cancer (CRC) has been reported heterogeneously across clinical trials. We conducted a systematic review and meta-analysis to evaluate the efficacy of ICIs in patients with advanced/metastatic CRC. Ovid-Medline was searched to identify clinical trials providing the efficacy outcomes of overall response rate (ORR) or disease control rate (DCR). The pooled ORR and DCR were estimated across all studies and subgroups. Meta-regression was performed to find the influencing factors for treatment efficacy. A total of thirty studies (1870 patients) were eligible. The overall ORR and DCR were 20.1% and 58.5%, respectively, but these results were heterogeneous across studies. Multivariate meta-regression revealed that microsatellite phenotype (odds ratio of MSI-H/dMMR versus MSS/pMMR: 1.67, p < 0.001) and drug regimen (odds ratio of monotherapy versus combination therapy: 1.07, p = 0.019) were the source of heterogeneity and also significantly influenced factors for the efficacy of the treatment. Although the efficacy of ICIs as a first-line therapy was higher than that of ICIs as the second- or more-line therapy (ORR: 51.5% vs. 13.4%, DCR: 85% vs. 49.5%), multivariate regression showed that the line of therapy was not a significant factor for the treatment efficacy. Our study suggests that the microsatellite phenotype and drug regimen, rather than the line of treatment, are the primary factors influencing the treatment response among advanced/metastatic CRC patients treated with an ICI-based regimen.

Immunotherapy in colorectal cancer: is the long-awaited revolution finally happening?

Immunotherapy has recently become a major treatment modality for several types of solid tumours, achieving remarkable and long-lasting remissions. In metastatic colorectal cancer patients (mCRC), immune checkpoint inhibitors (ICIs) were found to be effective as treatment for deficient mismatch repair (dMMR)/ microsatellite instability high (MSI-H) tumours and received regulatory approval for this indication. However, mCRC is a complex disease and dMMR/MSI-H tumours represent a minority of the cases; therefore, new strategies are needed to extend the benefits of immunotherapy to a larger population of patients. This review explores the immunological differences between dMMR/MSI-H and proficient mismatch repair (pMMR)/ microsatellite instability low (MSI-L) tumours, focuses on new proposed biomarkers to predict response to immunotherapy and illustrates results reported from the main clinical trials with immunotherapeutic agents in CRC, addressing the most promising approaches being currently developed.

PD-L1 targeting and subclonal immune escape mediated by PD-L1 mutations in metastatic colorectal cancer

BACKGROUND

In patients with microsatellite stable (MSS) metastatic colorectal cancer (mCRC), immune checkpoint blockade is ineffective, and combinatorial approaches enhancing immunogenicity need exploration.

METHODS

We treated 43 patients with predominantly microsatellite stable RAS/BRAF wild-type mCRC on a phase II trial combining chemotherapy with the epidermal growth factor receptor antibody cetuximab and the programmed cell death ligand 1 (PD-L1) antibody avelumab. We performed next-generation gene panel sequencing for mutational typing of tumors and liquid biopsy monitoring as well as digital droplet PCR to confirm individual mutations. Translational analyses included tissue immunohistochemistry, multispectral imaging and repertoire sequencing of tumor-infiltrating T cells. Detected PD-L1 mutations were mechanistically validated in CRISPR/Cas9-generated cell models using qRT-PCR, immunoblotting, flow cytometry, complement-dependent cytotoxicity assay, antibody-dependent cytotoxicity by natural killer cell degranulation assay and LDH release assay as well as live cell imaging of T cell mediated tumor cell killing.

RESULTS

Circulating tumor DNA showed rapid clearance in the majority of patients mirroring a high rate of early tumor shrinkage. In 3 of 13 patients expressing the high-affinity Fcγ receptor 3a (FcγR3a), tumor subclones with PD-L1 mutations were selected that led to loss of tumor PD-L1 by nonsense-mediated RNA decay in PD-L1 K162fs and protein degradation in PD-L1 L88S. As a consequence, avelumab binding and antibody-dependent cytotoxicity were impaired, while T cell killing of these variant clones was increased. Interestingly, PD-L1 mutant subclones showed slow selection dynamics reversing on avelumab withdrawal and patients with such subclones had above-average treatment benefit. This suggested that the PD-L1 mutations mediated resistance to direct antitumor effects of avelumab, while at the same time loss of PD-L1 reduced biological fitness by enhanced T cell killing limiting subclonal expansion.

CONCLUSION

The addition of avelumab to standard treatment appeared feasible and safe. PD-L1 mutations mediate subclonal immune escape to avelumab in some patients with mCRC expressing high-affinity FcγR3a, which may be a subset experiencing most selective pressure. Future trials evaluating the addition of avelumab to standard treatment in MSS mCRC are warranted especially in this patient subpopulation.

TRIAL REGISTRATION NUMBER

NCT03174405.

Beyond Microsatellite Instability: Evolving Strategies Integrating Immunotherapy for Microsatellite Stable Colorectal Cancer

OPINION STATEMENT

Advanced colorectal cancer (CRC) is a heterogeneous disease, characterized by several subtypes with distinctive genetic and epigenetic patterns. During the last years, immune checkpoint inhibitors (ICIs) have revamped the standard of care of several tumors such as non-small cell lung cancer and melanoma, highlighting the role of immune cells in tumor microenvironment (TME) and their impact on cancer progression and treatment efficacy. An "immunoscore," based on the percentage of two lymphocyte populations both at tumor core and invasive margin, has been shown to improve prediction of treatment outcome when added to UICC-TNM classification. To date, pembrolizumab, an anti-programmed death protein 1 (PD1) inhibitor, has gained approval as first-line therapy for mismatch-repair-deficient (dMMR) and microsatellite instability-high (MSI-H) advanced CRC. On the other hand, no reports of efficacy have been presented in mismatch-repair-proficient (pMMR) and microsatellite instability-low (MSI-L) or microsatellite stable (MSS) CRC. This group includes roughly 95% of all advanced CRC, and standard chemotherapy, in addition to anti-EGFR or anti-angiogenesis drugs, still represents first treatment choice. Hopefully, deeper understanding of CRC immune landscape and of the impact of specific genetic and epigenetic alterations on tumor immunogenicity might lead to the development of new drug combination strategies to overcome ICIs resistance in pMMR CRC, thus paving the way for immunotherapy even in this subgroup.

Perspectives on Immunotherapy of Metastatic Colorectal Cancer

Colorectal cancer, especially liver metastasis, is still a challenge worldwide. Traditional treatment such as surgery, chemotherapy and radiotherapy have been difficult to be further advanced. We need to develop new treatment methods to further improve the poor prognosis of these patients. The emergence of immunotherapy has brought light to mCRC patients, especially those with dMMR. Based on several large trials, some drugs (pembrolizumab, nivolumab) have been approved by US Food and Drug Administration to treat the patients diagnosed with dMMR tumors. However, immunotherapy has reached a bottleneck for other MSS tumors, with low response rate and poor PFS and OS. Therefore, more clinical trials are underway toward mCRC patients, especially those with MSS. This review is intended to summarize the existing clinical trials to illustrate the development of immunotherapy in mCRC patients, and to provide a new thinking for the direction and experimental design of immunotherapy in the future.

Immunotherapy in colorectal cancer

The immune tumor microenvironment (TME) of colorectal cancer (CRC) is a crucial contributor to disease biology, making it an important target for therapeutic intervention. The diversity of immune cell populations within various subsets of CRC has led to the discovery that immune characterization of the TME has both prognostic and predictive value for patients. The convergence of improved molecular and cellular characterization of CRC along with the widespread use of immunotherapy in solid tumors has led to a revolution in the approach to clinical care. Monoclonal antibodies (mAbs) which target key immune checkpoints, such as programmed death-1 (PD-1) and cytotoxic T-lymphocyte antigen 4 (CTLA-4), have demonstrated remarkable clinical activity in microsatellite instability-high (MSI-H) CRCs and are now used in routine practice. The observation that MSI-H cancers are highly infiltrated with immune cells and carry a high neoantigen load led to the successful targeting of these cancers with immunotherapy. More recently, the Food and Drug Administration (FDA) approved a PD-1 inhibitor for microsatellite stable (MSS) cancers with high tumor mutation burden. However, the anti-tumor activity of immunotherapy is rare in the majority of CRC. While immune cell characterization does provide prognostic value in these patients, these observations have not yet led to therapeutic interventions. By delineating factors that predict efficacy, resistance, and therapeutic targets, ongoing research will inform the development of effective combination strategies for the vast majority of MSS CRC and immunotherapy-resistant MSI-H cancers.

Chemotherapy agents stimulate dendritic cells against human colon cancer cells through upregulation of the transporter associated with antigen processing

Single immunotherapy fails to demonstrate efficacy in patients with microsatellite stable (MSS) metastatic colorectal cancer (mCRC). Research on immune reactions before and after systemic agents for mCRC is warranted. Our study examined cell line models to compare the expression of immune surface markers on colon cancer cells before and after chemotherapy agents. We also elucidated mechanisms underlying the effects of chemotherapy agents on immune surface markers. We used real-world clinical samples with NanoString analysis and the Perkin-Elmer Opal multiplex system. We established that chemotherapy agents, particularly 7-ethyl-10-hydroxycamptothecin (SN-38), the active metabolite of irinotecan, stimulated the expression of stimulatory MHC class I alleles through stimulation the pathway of transporters associated with antigen processing 1 and 2 (TAP1 and TAP2) in cell line models. Application of infected cell protein 47 (ICP-47), a specific inhibitor of the TAP1/TAP2, significantly inhibited expression of TAP1/TAP2 and also inhibited the expression of the downstream MHC class I. In the functional assay, SN-38 significantly promoted the phagocytosis of colon cancer cells by monocyte-derived dendritic cells (MoDCs). We confirmed that the expression of major histocompatibility complex (MHC) class I, significantly increased after first-line chemotherapy and targeted therapy in the samples of real-world patients with de novo mCRC. Our study provides new insights for novel immunotherapy combinations.

Avelumab and cetuximab as a therapeutic combination: An overview of scientific rationale and current clinical trials in cancer

Treatment outcomes have improved with the advent of immune checkpoint inhibitors and small molecule inhibitors. However, many patients do not respond with single agents. Consequently, ongoing research is focused on the use of combination therapies to increase clinical efficacy by potential synergistic effects. Here, we outline ongoing trials and review the rationale and evidence for the combination of avelumab, an anti-programmed death ligand 1 (PD-L1) immunoglobulin G1 (IgG1) monoclonal antibody (mAb), with cetuximab, an anti-epidermal growth factor receptor (EGFR) IgG1 mAb. Avelumab is approved as a monotherapy for the treatment of Merkel cell carcinoma and urothelial carcinoma, and in combination with axitinib for renal cell carcinoma; cetuximab is approved in combination with chemotherapy for the treatment of squamous cell carcinoma of the head and neck (SCCHN) and RAS wild-type metastatic colorectal cancer, and in combination with radiation therapy for SCCHN. Avelumab binds to PD-L1 expressed on tumor cells and immune regulatory cells, thus blocking its interaction with programmed death 1 and reventing T-cell suppression; cetuximab inhibits the EGFR signaling pathway, inhibiting proliferation and inducing apoptosis. Both therapies have complementary mechanisms of action and may also activate the immune system to induce innate effector function through the binding of their Fc regions to natural killer (NK) cells. Furthermore, cetuximab combined with chemotherapy has been shown to induce immunogenic cell death and leads to an increase in tumor-infiltrating CD8+ T and NK cells, which should synergize with the immunostimulatory effects of avelumab. Prospective studies will investigate this combination and inform future treatment strategies.

Angiogenesis Inhibitors for Colorectal Cancer. A Review of the Clinical Data

Since the late 1990s, therapy for metastatic colorectal cancer (mCRC) has changed considerably, and the combination of doublet or triplet chemotherapy and a targeted agent are now routinely used. The targeting of angiogenesis, the development of new blood vessels, represents a key element in the overall treatment strategy. Since the approval in 2004 of the first anti-angiogenetic drug, multiple agents have been approved and others are currently under investigation. We present an overview of the recent literature on approved systemic treatment of mCRC, with a focus on anti-angiogenic drugs, and current treatment approaches, and elaborate on the future role of angiogenesis in colorectal cancer as seen from a clinical perspective. The treatment of mCRC, in general, has changed from "one strategy fits all" to a more personalized approach. This is, however, not entirely the case for anti-angiogenetic treatments, partly due to a lack of validated biomarkers. The anti-angiogenetic standard treatment at the present primarily includes monoclonal antibodies. The therapeutic field of angiogenesis, however, has received increased interest after the introduction of newer combinations. These approaches will likely change the current treatment strategy, once again, to the overall benefit of patients.

An update on the use of immunotherapy in patients with colorectal cancer

Introduction: Colorectal cancer (CRC) is the third most common malignancy worldwide, with recent trends demonstrating increasing incidence amongst younger patients. Despite multiple treatment options, metastatic disease remains incurable. A new therapeutic strategy to harness the host immune system, specifically with immune checkpoint inhibitors, now has reported results from a number of clinical trials. Areas covered: This review will discuss in detail microsatellite instability (MSI) and other biomarkers for response to immunotherapy, summarize the pivotal clinical trials of immune checkpoint inhibitors in early-stage and metastatic MSI colorectal cancer, explore strategies to induce treatment responses in MSS CRC and highlight the emerging treatments and novel immune-based therapies under investigation. Expert opinion: Immunotherapy is now a standard of care for the proportion of CRC patients with MSI. While overall survival data are still awaited, the promise of profound and durable responses is highly anticipated. The lack of efficacy in MSS CRC is disappointing and strategies to convert these 'cold' tumors are needed. Further elucidation of optimal use of treatment sequences, combinations and novel agents will improve outcomes.

Immunotherapy in Colorectal Cancer: Current and Future Strategies

Despite the recent advances in the systemic treatment of metastatic colorectal cancer (mCRC), prognostic outcomes have remained to be poor. Thus, what is needed is an innovative treatment approach. Immune checkpoint inhibitors (ICIs) targeting programmed death-1 (PD-1) and anti-programmed cell death ligand 1 (PD-L1) have exhibited a durable response and dominated the treatment of various tumor types. However, in mCRC, the clinical benefit is limited in patients with deficient mismatch repair (dMMR)/high levels of microsatellite instability (MSI-H), comprising approximately 5% of mCRC cases, and some do not respond to ICI treatment. Thus, further research is needed to identify predictive biomarkers. The most urgent need is developing effective immunotherapy for patients with proficient mismatch repair (pMMR)/microsatellite stable (MSS) cancer, which comprises 95% of mCRC cases. Tumors with the pMMR/MSS phenotype often exhibit a lower tumor mutation burden and fewer tumor-infiltrating lymphocytes than dMMR/MSI-H, leading to immune tolerance and evasion in the tumor microenvironment. Therefore, a number of investigative studies aimed at overcoming tumor resistance in current immunotherapy approaches are underway. A better understanding on the complexity and diversity of the immune system's functioning within the tumor microenvironment will increase the potential for developing predictive biomarkers and novel therapeutic strategies to potentiate anti-tumor immunity in patients with mCRC. In this review, we summarize the most recent advances in immunotherapy based on the findings of pivotal clinical trials for patients with mCRC, highlighting potent therapeutic approaches and predictive biomarkers.

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.

Effective management of advanced colon cancer genotyping microsatellite stable/microsatellite instable-low with Kirsten rat sarcoma viral oncogene mutation using nivolumab plus ipilimumab combined with regorafenib and irinotecan: A case report

Microsatellite stable /microsatellite instable-low is the most common colorectal cancer genotype, counting for approximately 85% of common colorectal cancer patients. Treatment of advanced microsatellite stable/microsatellite instable-low colorectal cancer is difficult and successful pharmacological treatment options are currently lacking. Here, we report a case of a 37-year-old man with advanced colorectal cancer genotyping microsatellite stable/microsatellite instable-low with a Kirsten rat sarcoma viral oncogene (G12V) mutation. Following palliative surgery, the patient did not response to the common recommended chemotherapy FOLFIRI regimen and other chemotherapy options. Finally, the patient was successfully treated using a unique combinational immunotherapy, using nivolumab plus ipilimumab combined with regorafenib and irinotecan. Significant improvement in the Karnofsky Performance Status scores, liver function and well-being, reduction in serum tumor biomarkers, and reduction in the size of multiple liver metastatic tumors was evident. This report provides a rare case in which a unique and effective combinational immunotherapy for refractory advanced colon cancer patients is discussed. It encourages further research into combined immunotherapy for immuno-insensitive colon cancer patients.

Mechanisms of Immunosuppression in Colorectal Cancer

Simple Summary

More emerging studies are exploring immunotherapy for solid cancers, including colorectal cancer. Besides, checkpoint blockade immunotherapy and chimeric antigen receptor (CAR) -based immune cell therapy have being examined in clinical trials for colorectal cancer patients. However, immunosuppression that leads to the blockage of normal immunosurveillance often leads to cancer development and relapse. In this study, we systematically reviewed the mechanism of immunosuppression, specifically in colorectal cancer, from different perspectives, including the natural or induced immunosuppressive cells, cell surface protein, cytokines/chemokines, transcriptional factors, metabolic alteration, phosphatase, and tissue hypoxia in the tumor microenvironment. We also discussed the progress of immunotherapies in clinical trials/studies for colorectal cancer and highlighted how different strategies for cancer therapy targeted the immunosuppression reviewed above. Our review provides some timely implications for restoring immunosurveillance to improve treatment efficacy in colorectal cancer (CRC).

Abstract

CRC is the third most diagnosed cancer in the US with the second-highest mortality rate. A multi-modality approach with surgery/chemotherapy is used in patients with early stages of colon cancer. Radiation therapy is added to the armamentarium in patients with locally advanced rectal cancer. While some patients with metastatic CRC are cured, the majority remain incurable and receive palliative chemotherapy as the standard of care. Recently, immune checkpoint blockade has emerged as a promising treatment for many solid tumors, including CRC with microsatellite instability. However, it has not been effective for microsatellite stable CRC. Here, main mechanisms of immunosuppression in CRC will be discussed, aiming to provide some insights for restoring immunosurveillance to improve treatment efficacy in CRC.

The Efficacy and Safety of Regorafenib in Combination With Anti-PD-1 Antibody in Refractory Microsatellite Stable Metastatic Colorectal Cancer: A Retrospective Study

Background

Microsatellite stable (MSS) or mismatch repair proficient (pMMR) metastatic colorectal cancer (mCRC) is resistant to immune checkpoint inhibitors. However, a recent Japanese trial showed that regorafenib plus nivolumab had encouraging anti-cancer activity in MSS or pMMR mCRCs.

Materials and Methods

We retrospectively reviewed the efficacy and safety data of combination therapy with regorafenib plus anti-PD-1 antibody in patients with refractory MSS or pMMR mCRC in the medical centers of Shandong Province in China.

Results

Twenty-three patients with MSS or pMMR mCRC received regorafenib plus anti-PD-1 antibody. Eighteen (78.3%) patients experienced stable disease as best response, five (21.7%) patients had progressive disease, and no partial response was observed. The disease control rate (DCR) was 78.3% (18/23), and the median progression-free survival (PFS) was 3.1 months (95% CI, 2.32-3.89). Four of five (80.0%) patients with progressive disease had baseline liver metastasis, while nine of 18 (50.0%) patients with stable disease displayed no liver metastasis. One patient receiving radiofrequency ablation treatment for liver and abdominal wall metastases prior to combination treatment experienced a remarkably prolonged PFS of 9.2 months with SD. Neither liver metastasis status nor previous exposure to regorafenib was associated with treatment outcome. Treatment-related grade 3 toxicities were observed in 5/23 (21.7%) patients.

Conclusion

No objective response was observed with the combination of regorafenib plus anti-PD-1 antibody, suggesting its little clinical activity in unselected Chinese patients with pMMR/MSS mCRC. Meanwhile, it exhibited some potential benefit in this cohort in terms of DCR and PFS. Adverse events were generally tolerable and manageable. Prospective studies with large sample sizes are needed to verify the findings. This combination strategy plus local ablative therapy might be worthy of further exploration.

Augmenting Anticancer Immunity Through Combined Targeting of Angiogenic and PD-1/PD-L1 Pathways: Challenges and Opportunities

Cancer immunotherapy (CIT) with antibodies targeting the programmed cell death 1 protein (PD-1)/programmed cell death 1 ligand 1 (PD-L1) axis have changed the standard of care in multiple cancers. However, durable antitumor responses have been observed in only a minority of patients, indicating the presence of other inhibitory mechanisms that act to restrain anticancer immunity. Therefore, new therapeutic strategies targeted against other immune suppressive mechanisms are needed to enhance anticancer immunity and maximize the clinical benefit of CIT in patients who are resistant to immune checkpoint inhibition. Preclinical and clinical studies have identified abnormalities in the tumor microenvironment (TME) that can negatively impact the efficacy of PD-1/PD-L1 blockade. Angiogenic factors such as vascular endothelial growth factor (VEGF) drive immunosuppression in the TME by inducing vascular abnormalities, suppressing antigen presentation and immune effector cells, or augmenting the immune suppressive activity of regulatory T cells, myeloid-derived suppressor cells, and tumor-associated macrophages. In turn, immunosuppressive cells can drive angiogenesis, thereby creating a vicious cycle of suppressed antitumor immunity. VEGF-mediated immune suppression in the TME and its negative impact on the efficacy of CIT provide a therapeutic rationale to combine PD-1/PD-L1 antibodies with anti-VEGF drugs in order to normalize the TME. A multitude of clinical trials have been initiated to evaluate combinations of a PD-1/PD-L1 antibody with an anti-VEGF in a variety of cancers. Recently, the positive results from five Phase III studies in non-small cell lung cancer (adenocarcinoma), renal cell carcinoma, and hepatocellular carcinoma have shown that combinations of PD-1/PD-L1 antibodies and anti-VEGF agents significantly improved clinical outcomes compared with respective standards of care. Such combinations have been approved by health authorities and are now standard treatment options for renal cell carcinoma, non-small cell lung cancer, and hepatocellular carcinoma. A plethora of other randomized studies of similar combinations are currently ongoing. Here, we discuss the principle mechanisms of VEGF-mediated immunosuppression studied in preclinical models or as part of translational clinical studies. We also discuss data from recently reported randomized clinical trials. Finally, we discuss how these concepts and approaches can be further incorporated into clinical practice to improve immunotherapy outcomes for patients with cancer.

Current Status and Future Perspective of Immunotherapy in Gastrointestinal Cancers

Gastrointestinal (GI) cancers represent a major public health problem worldwide. Due to the late detection and high heterogeneity of GI cancers, traditional treatments, including surgery, radiotherapy, chemotherapy, and targeted therapy, have shown limited effects, and the overall prognosis of these patients remains poor. Recently, immunotherapy, involving programmed cell death-1 (PD-1) and its ligand (PD-L1), has shown promising efficacy in several solid cancers and seems to have become a potential treatment option for GI cancers This review focuses on data on the development of immunotherapy-based clinical trials in esophageal cancer, gastric cancer, and colorectal cancer. The predictive biomarkers and combination strategies in clinical trials and translational medicine are also discussed. Finally, prospects for immunotherapy in the treatment of GI cancers are described. Although only a small proportion of patients with GI cancers respond to PD-1/PD-L1 blockade, we strongly believe that precision immunotherapy might improve the overall survival of many more GI cancer patients in the future.