Background: Intestinal microbiota play a critical role in the development of colorectal cancer. However, little is known about the structure and characteristics of gut microbial in colorectal cancer, especially in locally advanced rectal cancer after neoadjuvant chemoradiation therapy.
Methods: Here, we performed this study to evaluate microbial characteristics between pathologic complete response (pCR) (n=12) and non-pathological complete response (Non-pCR) (n=45) tumor tissues from patients with locally advanced rectal cancer after neoadjuvant chemoradiation therapy. In this study, 16S rRNA gene sequencing was used to detect the microbial diversity including Alpha diversity and Beta diversity. Moreover, we used PICRUSt from the Kyoto Encyclopedia of Genes and Genomes (KEGG) database to predict the microbial metabolism functions.
Results: There was significant statistical difference in PFS between pCR and Non-pCR group (p < 0.05). However, there was no significant difference in OS between pCR and Non-pCR group. The microbial compositions in the both groups were Proteobacteria, Actinobacteria, Firmicutes  and Thermi  and Bacteroidetes  at the phylum level. The five most predominant genera in both pCR and Non-pCR tissue groups were Sphingobium, Acinetobacter, Cupriavidus, Thermi  and Sphingomonas  at the genus level. The key taxa identified in the pCR and Non-pCR tissues were Thermi  and Sphingomonadaceae  respectively. In addition, a series of human disease-related genes were also significantly different between pCR and Non-pCR group.
Conclusion: In summary, we demonstrated the characteristic differences in microbial communities between pCR tissues and Non-pCR tumor tissues from locally advanced rectal cancer patients after neoadjuvant chemoradiation therapy. Our results present new alterations in the microbiome in locally advanced rectal cancer after neoadjuvant chemoradiation therapy, suggesting that it will provide a new perspective for the precise treatment of neoadjuvant rectal cancer by targeting specific microbial species in the future.
Keywords: intestinal microbial, 16S rRNA gene sequencing, pathologic complete response, neoadjuvant chemoradiation therapy, colorectal cancer