Third line treatment of advanced oesophagogastric cancer: A critical review of current evidence and evolving trends

There is increasing evidence that treatment beyond second line provides significant survival benefit for selected advanced oesophageal and gastric adenocarcinoma patients, and important randomised controlled trials of both chemotherapy, targeted therapy and immunotherapy have recently been reported in this space. Despite this growing evidence base there are presently no formal guidelines for third line treatment available to clinicians, and as these agents move into routine clinical practice patient selection and rational sequencing of treatment will become an increasingly relevant clinical challenge. This review critically appraises the current evidence base for third line treatment and discusses patient selection, potential predictive biomarkers and future directions for third line treatment in this challenging condition.

Pembrolizumab for the treatment of gastric cancer

INTRODUCTION

Gastric cancer is one of a few gastrointestinal malignancies in which immunotherapy has shown meaningful activity. Pembrolizumab is the first and only immune checkpoint inhibitor to be FDA-approved in gastric cancer. Areas Covered: This review summarizes the current and emerging clinical evidence for immune checkpoint inhibitors in advanced and metastatic gastric cancer, with a focus on pembrolizumab. Expert Commentary: Pembrolizumab has shown impressive activity in the third-line treatment of locally advanced and metastatic gastric cancer. It is currently being studied as upfront therapy in combination with chemotherapy. The emerging understanding of the molecular alterations and tumor immune microenvironment as predictors of immunotherapy response in gastric cancer are discussed. The impact of gastric mucosal dysbiosis on gastric carcinogenesis and the modulation of immunotherapy response by the gut microbiome are also reviewed.

Prognostic significance of tumor immune microenvironment and immunotherapy: Novel insights and future perspectives in gastric cancer

Despite a decrease in gastric cancer incidence, the development of novel biologic agents and combined therapeutic strategies, the prognosis of gastric cancer remains poor. Recently, the introduction of modern immunotherapy, especially using immune checkpoint inhibitors, led to an improved prognosis in many cancers. The use of immunotherapy was also associated with manageable adverse event profiles and promising results in the treatment of patients with gastric cancer, especially in heavily pretreated patients. These data have led to an accelerated approval of some checkpoint inhibitors in this setting. Understanding the complex relationship between the host immune microenvironment and tumor and the immune escape phenomenon leading to cancer occurrence and progression will subsequently lead to the identification of prognostic immune markers. Furthermore, this understanding will result in the discovery of both new mechanisms for blocking tumor immunosuppressive signals and pathways to stimulate the local immune response by targeting and modulating different subsets of immune cells. Due to the molecular heterogeneity of gastric cancers associated with different clinico-biologic parameters, immune markers expression and prognosis, novel immunotherapy algorithms should be personalized and addressed to selected subsets of gastric tumors, which have been proven to elicit the best clinical responses. Future perspectives in the treatment of gastric cancer include tailored dual immunotherapies or a combination of immunotherapy with other targeted agents with synergistic antitumor effects.

Advances in molecular, genetic and immune signatures of gastric cancer: Are we ready to apply them in our patients' decision making?

In the last few years we have witnessed a vast expansion of our knowledge regarding the molecular and genetic profile of gastric cancer. The molecular subtypes described have shed light on the pathogenesis of the disease, thus prompting the development of new therapeutic strategies and favoring a more individualized approach for treatment. Most of the clinical trials for so called targeted therapies could be considered, at best, partially successful. In addition, checkpoint inhibitors have recently been added to our armamentarium in later stages of the disease, and combinations with chemotherapy and targeted agents are currently under development. In view of the rapid advances of molecular oncology, a new challenge for the clinical oncologist arises: The appropriate patient selection for each new therapy, which can be made possible only through the implementation of predictive biomarkers in our therapy decision making.

Immunotherapy for Gastric Cancer: Time for a Personalized Approach?

Over the last decade, our understanding of the mechanisms underlying immune modulation has greatly improved, allowing for the development of multiple therapeutic approaches that are revolutionizing the treatment of cancer. Immunotherapy for gastric cancer (GC) is still in the early phases but is rapidly evolving. Recently, multi-platform molecular analyses of GC have proposed a new classification of this heterogeneous group of tumors, highlighting subset-specific features that may more reliably inform therapeutic choices, including the use of new immunotherapeutic drugs. The clinical benefit and improved survival observed in GC patients treated with immunotherapeutic strategies and their combination with conventional therapies highlighted the importance of the immune environment surrounding the tumor. A thorough investigation of the tumor microenvironment and the complex and dynamic interaction between immune cells and tumor cells is a fundamental requirement for the rational design of novel and more effective immunotherapeutic approaches. This review summarizes the pre-clinical and clinical results obtained so far with immunomodulatory and immunotherapeutic treatments for GC and discusses the novel combination strategies that are being investigated to improve the personalization and efficacy of GC immunotherapy.

Evolving Management Strategies for Metastatic Esophageal and Gastroesophageal Junction Adenocarcinoma

Metastatic or unresectable esophageal and gastroesophageal junction adenocarcinoma represent a devastating disease with 5-year survival rate of <5%. Although cytotoxic chemotherapy with platinum-doublet-based regimens is initially effective, patients inevitably progress. Patients often decline rapidly after this initial progression, making later lines of therapy a challenge to successfully administer There have been multiple efforts to incorporate biologic agents, targeting pathways known to be dysregulated in esophageal adenocarcinoma and gastroesophageal junction adenocarcinoma, into existing chemotherapy backbones. Other than therapeutics targeting human epidermal growth factor receptor-2 (HER2) and vascular endothelial growth factor receptor (VEGFR), other strategies have failed. Given the mixed success of biologic agents, along with the promise of immunotherapy to generate durable and sometimes complete responses, immune-agent based trials are a major area of interest for patients with this disease. Checkpoint inhibitors blocking programmed cell death protein 1 (PD-1) and programmed death-ligand 1 (PD-L1) have demonstrated modest single-agent efficacy in patients with progressive esophageal adenocarcinoma and gastroesophageal junction adenocarcinoma. However, other approaches such as novel checkpoint combinations, vaccine-based approaches and autologous T cells hold more promise to change the trajectory of disease.

Pembrolizumab for treatment of advanced gastric and gastroesophageal junction adenocarcinoma

Pembrolizumab is a monoclonal antibody directed against PD-1 that is US FDA approved for treatment of advanced PD-L1 positive gastric and gastroesophageal junction adenocarcinoma in patients who have progressed on at least two prior lines of chemotherapy. This article summarizes the clinical evidence regarding safety, tolerability and efficacy of pembrolizumab in this setting. In addition, this article describes the investigational use of pembrolizumab as first- and second-line therapy and in combination with other treatments. Finally, this review compares other checkpoint inhibitors to pembrolizumab for the treatment of this disease, and explores predictive biomarkers of response to PD-1 blockade.