The Role of Toll-like Receptors in Esophageal Cancer

Esophageal adenocarcinoma (AC) develops through Barrett's esophagus (BE) and columnar dysplasia, preceded by gastro-esophageal reflux disease (GERD). Incidence of esophageal squamous cell carcinoma (SCC) is increased with tobacco smoking and alcohol abuse. Toll-like receptors (TLRs) can act as prognostic factors and potential therapeutic targets of esophageal cancer. TLRs, an important family of pattern recognition receptors, allow immune cells to recognize pathogens triggering inflammation. TLR-signaling pathway activates signaling-elements, regulating inflammatory response, possibly correlating to carcinogenesis. In the normal esophagus, TLRs recognize molecular patterns on microorganisms and inflammatory response produced by tissue-damage. TLR3, TLR4, TLR5, and TLR9 are expressed at increasing levels from GERD to AC. TLR4 is a mediator of proliferation in AC, while TRL1 and TLR4 over-expression in AC is related to poor prognosis and metastasis. Additionally, TLR3, TLR4, and TLR9 expression in SCC has been associated with lymphatic metastasis, whereas increased expression of TLR7 and TLR9 has been also associated with advanced disease. It seems that TLR expression can indicate esophageal metaplasia, dysplasia, and cancer. Herein, we aimed to present all available data regarding the relation of TLRs and esophageal cancer. They may represent significant and valuable diagnostic or prognostic factors for esophageal cancer.