Abstract PO3-09-03: Dysbiosis of gut microbiota in patients with breast cancer

Abstract Background The effects of gut microbiome on various diseases have become widely known, and many studies reported that there was a correlation between the change of gut microbiota, that is dysbiosis, and the progression of digestive tract cancer. In addition, it is well-known that gut microbiota was correlated to the efficacy of immune checkpoint inhibitors for multiple types of cancer. However, the significance of gut microbiota in patients with breast cancer still remains unclear. The aim of this study is to analyze the gut microbiota in patients with breast cancer, compared with healthy women. Subjects and Methods We used the pre-treatment feces of 79 patients with primary breast cancer who received treatment at our facility and performed metagenome analysis of the V3-4 region of 16S rDNA. We also analyzed the breast cancer patients' microbiota with QIIME2 analysis method, compared to randomly selected 100 women aged 30-77 years from NIBIOHN's public data . We also assessed the characteristics of the gut microbiota of breast cancer patients by subtypes and its relationship with clinical and pathological factors. Results In Japanese gut microbiota, the Firmicutes and Bacteroidetes phyla make up the majority, but Firmicutes was the most common bacterial phylum in 52% of the public cohort, whereas 96.2% (76/79) of the breast cancer patients’ group (BC) showed a significantly higher proportion (p 0.0001). In addition, ANCOM analysis revealed that the relative bacterial amounts of the Firmicutes, Bacteroidetes, and Proteobacteria phyla were significantly decreased in BC compared to the public cohort (PC), and at the bacterial genus level, the Feacalibacterium genus was significantly decreased in BC. Furthermore, the percentage of Fusobacteria phylum, which is a well-known oral bacteria that exacerbates digestive tract cancer, was 49.3% in BC, compared to 35% in PC (p=0.04). Among BC, the relative frequency of Fusobacteria phylum was significantly higher in the HER2-negative group than in the HER2-positive group (p 0.0001). In BC, both alpha diversity (p 0.0001) and beta diversity (p=0.001) were significantly lower than in PC. Conclusion An increase in the Firmicutes phylum is known to be associated with obesity, and also likely to affect the incidence risk of breast cancer. The results suggest that the Fusobacteria phylum and Feacalibacterium genus may be risk or preventive factors for breast cancer. Dysbiosis of gut microbiota is suggested to be associated with various diseases, and in this study the decrease in bacterial amount and diversity was observed in BC compared to PC, which may affect the onset and progression of breast cancer. Citation Format: Mai Yamada, Takafumi Morisaki, Yo Sato, Kimihisa Mizoguchi, Yuka Takao, Yurina Ochiai, Yoshiki Ootubo, Saori Hayashi, Masafumi Nakamura, Makoto Kubo. Dysbiosis of gut microbiota in patients with breast cancer abstract. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO3-09-03.