Molecular Pathology of Gastroesophageal Cancer

The Landscape and Prognosis of Microsatellite Stable (MSS) Esophageal, Gastro-Esophageal Junction and Gastric Adenocarcinomas with High Tumor Mutation Burden (TMB)

BACKGROUND

A minority of patients with MSS tumors present a high tumor mutation burden (TMB) without underlying MMR defects.

METHODS

Publicly available genomic series were assessed for identification of patients with MSS gastric gastroesophageal junction, and esophageal adenocarcinomas and a high TMB, defined as more than 10 mutations per Mb. These were compared with MSS cancers and a low TMB for genetic alterations and for survival outcomes.

RESULTS

Patients with MSS cancers with high TMB in the MSK series were older but did not differ in other clinicopathologic parameters compared with MSS patients with low TMB. Mutations in tumor suppressors TP53 and APC and oncogenes KRAS and ERBB4 as well as amplifications of ERBB2 were more prevalent in the high TMB group of MSS cancers. Mutations in DDR associated genes, in epigenetic modifiers and in genes associated with immune response were more prevalent in the hIgh TMB group patients. However, high TMB was not associated with an improved survival in MSS gastric/gastroesophageal junction/esophageal adenocarcinomas (Log Rank p = 0.5).

CONCLUSION

MSS Gastric/gastroesophageal junction/esophageal adenocarcinomas with TMB above 10 mutations per Mb possess a genomic landscape with increased alteration frequencies in common gastroesophageal cancer genes and pathways.

The preclinical discovery and development of zolbetuximab for the treatment of gastric cancer

INTRODUCTION

Gastric cancer remains a formidable challenge in oncology with high mortality rates and few advancements in treatment. Claudin-18.2 (CLDN18.2) is a tight junction protein primarily expressed in the stomach and is frequently overexpressed in certain subsets of gastric cancers. Targeting CLDN18.2 with monoclonal antibodies, such as zolbetuximab (IMAB362), has shown promising efficacy results in combination with chemotherapy.

AREAS COVERED

The molecular cell biology of CLDN18.2 is discussed along with studies demonstrating the utility of CLDN18.2 expression as a biomarker and therapeutic target. Important clinical studies are reviewed, including Phase III trials, SPOTLIGHT and GLOW, which demonstrate the efficacy of zolbetuximab in combination with chemotherapy in patients with CLDN18.2-positive advanced gastric cancer.

EXPERT OPINION

CLDN18.2 is involved in gastric differentiation through maintenance of epithelial barrier function and coordination of signaling pathways, and its expression in gastric cancers reflects a 'gastric differentiation' program. Targeting Claudin-18.2 represents the first gastric cancer specific 'targeted' treatment. Further studies are needed to determine its role within current gastric cancer treatment sequencing, including HER2-targeted therapies and immunotherapies. Management strategies will also be needed to better mitigate zolbetuximab-related treatment side effects, including gastrointestinal (GI) toxicities.

The role of the fibroblast in Barrett's esophagus and esophageal adenocarcinoma

PURPOSE OF REVIEW

Barrett's esophagus (BE) is the number one risk factor for developing esophageal adenocarcinoma (EAC), a deadly cancer with limited treatment options that has been increasing in incidence in the US. In this report, we discuss current studies on the role of mesenchyme and cancer-associated fibroblasts (CAFs) in BE and EAC, and we highlight translational prospects of targeting these cells.

RECENT FINDINGS

New insights through studies using single-cell RNA sequencing (sc-RNA seq) have revealed an important emerging role of the mesenchyme in developmental signaling and cancer initiation. BE and EAC share similar stromal gene expression, as functional classifications of nonepithelial cells in BE show a remarkable similarity to EAC CAFs. Several recent sc-RNA seq studies and novel organoid fibroblast co-culture systems have characterized the subgroups of fibroblasts in BE and EAC, and have shown that these cells can directly influence the epithelium to induce BE development and cancer progression. Targeting the CAFs in EAC with may be a promising novel therapeutic strategy.

SUMMARY

The fibroblasts in the surrounding mesenchyme may have a direct role in influencing altered epithelial plasticity during BE development and progression to EAC.

Molecular pathogenesis, targeted therapies, and future perspectives for gastric cancer

Gastric cancer is a major source of global cancer mortality with limited treatment options and poor patient survival. As our molecular understanding of gastric cancer improves, we are now beginning to recognize that these cancers are a heterogeneous group of diseases with incredibly unique pathogeneses and active oncogenic pathways. It is this molecular diversity and oftentimes lack of common oncogenic driver mutations that bestow the poor treatment responses that oncologists often face when treating gastric cancer. In this review, we will examine the treatments for gastric cancer including up-to-date molecularly targeted therapies and immunotherapies. We will then review the molecular subtypes of gastric cancer to highlight the diversity seen in this disease. We will then shift our discussion to basic science and gastric cancer mouse models as tools to study gastric cancer molecular heterogeneity. Furthermore, we will elaborate on a molecular process termed paligenosis and the cyclical hit model as key events during gastric cancer initiation that impart nondividing mature differentiated cells the ability to re-enter the cell cycle and accumulate disparate genomic mutations during years of chronic inflammation and injury. As our basic science understanding of gastric cancer advances, so too must our translational and clinical efforts. We will end with a discussion regarding single-cell molecular analyses and cancer organoid technologies as future translational avenues to advance our understanding of gastric cancer heterogeneity and to design precision-based gastric cancer treatments. Elucidation of interpatient and intratumor heterogeneity is the only way to advance future cancer prevention, diagnoses and treatment.

Inhibition MNK-eIF4E-β-catenin preferentially sensitizes gastric cancer to chemotherapy

Aberrant activation of eIF4E contributes to gastric cancer growth and resistance. MAPK-interacting kinases (MNKs) regulate eIF4E phosphorylation and activity in tumor but not normal cells and are potentially safe targets for the treatment of various cancers. Our work reveals that tomivosertib, a potent and highly selective dual MNK1/2 inhibitor, preferentially sensitizes gastric cancer to chemotherapy via suppressing MNK-eIF4E-β-catenin. We firstly demonstrate that tomivosertib displays higher efficacy than other MNK inhibitors in inhibiting gastric cancer cells. In addition, tomivosertib significantly augments the inhibitory effects of 5-FU and paclitaxel but not everolimus, suggesting that tomivosertib preferentially sensitizes gastric cancer to chemotherapy. We next show that eIF4E overexpression and phosphorylation coordinately regulate β-catenin signaling in gastric cancer. Rescue studies confirm that tomivosertib inhibits gastric cancer via targeting MNK- eIF4E-β-catenin. Finally, we demonstrate that the in vitro functional and mechanism observations are translatable to in vivo gastric cancer model in mice. Tomivosertib is now in Phase 2 clinical trials. Our study provides preclinical evidence to initialize clinical trials for gastric cancer using tomivosertib in combination with chemotherapy.