Mesothelin expression in esophageal adenocarcinoma and squamous cell carcinoma and its possible impact on future treatment strategies

Background

Mesothelin is expressed at very low levels by normal mesothelial cells but is overexpressed in several human cancers. This makes mesothelin a promising target for immunotherapy. Limited data exist about mesothelin expression in esophageal carcinoma. In a current clinical trial, the highly potent anti-mesothelin antibody anetumab ravtansine is used in patients with mesothelin-positive tumors. Response rates are correlated with mesothelin expression (using the Ventana antibody) in tumor cells. No data are available on expression levels using the Ventana antibody. Most data have been generated using the Novocastra antibody. As patients are selected for clinical trials based on antibody staining of tumor samples, a comparison of these two available antibodies is crucial.

Methods

We analyzed 481 esophageal carcinomas [373 esophageal adenocarcinomas (EACs), 108 esophageal squamous cell carcinomas (ESCCs)] using two different monoclonal antibodies (Novocastra and Ventana) for mesothelin expression (low-mid and high-level expression, as used in one clinical trial). We also checked for the correlation of these results with clinical and molecular data.

Results

We revealed different staining results for both antibodies in EACs: Ventana: 53.6% (low expression: 25.3%; high expression: 28.3%) and Novocastra: 35.7% (low expression: 21.2%; high expression 14.5%). In ESCC we found comparable staining results: Ventana: 13.3% (low expression: 9.5%; high expression: 3.8%) and Novocastra: 13% (low expression: 11.1%; high expression: 1.9%). ARID1a-deficient EAC patients demonstrated significantly higher rates of mesothelin-positive tumors than ARID1a intact EAC patients. No correlations were found with other molecular alterations (TP53 mutation, ERBB2 amplification) or survival rates.

Conclusion

To the best of our knowledge, this is the largest study analyzing the importance of mesothelin expression in esophageal carcinoma. This study revealed a significant number of mesothelin-positive esophageal carcinomas, especially adenocarcinomas. New therapeutic targets are urgently required to improve the outcome of patients with locally advanced or metastasized esophageal carcinoma. The inhibition of mesothelin can be a new attractive target.

Novel insights into mesothelioma biology and implications for therapy

Malignant mesothelioma is a universally lethal cancer that is increasing in incidence worldwide. There is a dearth of effective therapies, with only one treatment (pemetrexed and cisplatin combination chemotherapy) approved in the past 13 years. However, the past 5 years have witnessed an exponential growth in our understanding of mesothelioma pathobiology, which is set to revolutionize therapeutic strategies. From a genomic standpoint, mesothelioma is characterized by a preponderance of tumour suppressor alterations, for which novel therapies are currently in development. Other promising antitumour agents include inhibitors against angiogenesis, mesothelin and immune checkpoints, which are at various phases of clinical trial testing.