Evolution of Resident Microbiota in Gastroesophageal carcinogenesis

Esophageal cancer is now the seventh malignancy in terms of incidence in the worldwide ranking and the sixth in mortality. Esophageal adenocarcinoma (EAC) and squamous cell carcinoma (ESCC) are the two histological types, which are most frequent. Although the incidence of ESCC is declining in the last few years, the same is not true for EAC, especially in Western countries. The age of EAC onset is between 50-60 years and it is more frequent in males. EAC is usually asymptomatic until an advanced disease stage when symptoms appear. EAC often develops after a long-standing gastroesophageal reflux disease (GERD) and its principal precursor is Barrett's esophagus which is a specialized metaplasia of the epithelium of the lower esophagus. BE is considered the main risk factor since most cases of EAC arise in the background of BE. Although the incidence of gastric cancer (GC) decreases over the last few years, it remains high worldwide and GC is the fifth most commonly diagnosed cancer type in 2018 and the fourth for mortality globally. Gastric adenocarcinoma is the most frequent subtype, comprising 95% of the total number of GC. GC develops through a cascade of lesions starting with severe atrophic gastritis (AG), often correlated to Helicobacter pylori infection. Despite technical advances in surgery and the use of adjuvant therapy, the overall 5-year survival rate of EAC and GC remains poor, since the diagnosis occurs at the late stage of the disease. In recent years new data suggest the possible important role of resident gastroesophageal microbiota in the progression from pre-neoplastic lesions to adenocarcinoma, both gastric and esophageal. This project aimed to investigate gastroesophageal microbiota in patients affected by pre-cancerous lesions (BE and AG), dysplastic lesions (low and high-grade dysplasia) and cancer (GC and EAC), to identify bacteria possibly involved in carcinogenesis and to evaluate if resident microbiota analysis could lead to developing a multiparametric score that could be used in clinical practice to stratify cancer progression risk. Consecutive patients undergoing upper endoscopy within an endoscopic follow-up protocol for the presence of BE (Discovery cohort 1, DC1) or AG (Discovery cohort 2, DC2) were considered. Biopsies from the distal esophagus, antrum, and corpus were collected during endoscopy. The microbiota was analysed by amplification and sequencing of the hypervariable region V3-V4 from the 16S ribosomal RNA gene. Sequencing was carried out using Illumina Technology and bioinformatic analyses were performed with CLC Genomics Workbench. The composition of the bacterial community inhabiting the distal esophagus of our patients in DC1 was evaluated at each different taxonomic level in the distal esophageal biopsies along the disease progression. The parallel decrease in the relative abundance of Streptococcus and the increase in several bacteria belonging to the Proteobacteria phylum along the disease progression confirmed the shift in microbial composition already shown in other previous studies. The same analyses were performed in patients included in DC2, evaluating at each different taxonomic level the composition of bacteria colonizing both the antrum and corpus biopsies along the disease progression. To further investigate bacteria potentially associated with cancer development, non-dysplastic patients and dysplastic/cancer patients were compared. Thanks to this analysis, performed on both DC1 and DC2, it was possible to identify bacteria potentially involved in carcinogenesis and calculate a multiparametric score, able, with high sensitivity, to predict the risk of progression towards GC and EAC in patients affected by the pre-neoplastic lesion. The development of microbiome-based risk prediction models for both esophageal and gastric cancer, could open new research avenues, demonstrating that the resident microbiome may be a valid cancer risk biomarker.