Breast cancer (BC) is the most commonly diagnosed cancer and the second cause of cancer-specific death in women worldwide. Increasing evidence suggests that gut microbial dysbiosis may have a role to play in the pathogenesis, treatment and prognosis of BC.
The “BiotaCancerSurvivors” was a prospective, longitudinal, observational, unicentric and case-control study that aimed to analyse whether the gut microbiota differs between cancer survivors and a database of healthy controls. In this first analysis, samples from 23 BC survivors (group 1) and 291 healthy female controls (group 2) were characterised through the V3 and V4 regions that encode the “16S rRNA” gene of each bacteria. The samples were sequenced by Next Generation Sequencing (NGS), and the taxonomy was identified by resorting to Kraken2 and improved with Bracken, using a curated database called 'GutHealth_DB'. The α and β-diversity analyses were used to determine the gut microbiota's richness and evenness. Mann-Whitney U test was applied to assess differential abundance between both groups. Firmicutes/Bacteroidetes ratio was calculated using Kruskal-Wallis chi-squared test.
The α-diversity was significantly higher in group 1 (p=.28e-12 for the Chao index and p= 1.64e-12 for the ACE index). Shannon index wasn't statistically different between the two groups (p=.72). The microbiota composition was different between both groups: a null hypothesis was rejected for PERMANOVA (p=9.99e-05) and Anosim (p=.04) and was not rejected for β-dispersion (p=.158), using Unifrac weighted distance. Relative abundance of 14 phyla, 29 classes, 25 orders, 64 families, 116 genera and 74 species differed significantly between both groups. F/B ratio was signicantly lower in group 1 than in group 2, p<0.001.
We observed significant taxonomic disparities between BC survivors and healthy controls. Additional studies are needed to clarify the involved mechanisms and explore the relationship between microbiota and BC survivorship. Still, the data we possess so far, instills a need for further exploration of this field, given the potential microbiota role as a prognostic biomarker for BC survivorship.
We want to thank CUF Oncologia and to all voluntary women enrolled in the BiotaCancerSurvivors study.
The authors.
Has not received any funding.
D. Alpuim Costa: Financial Interests, Institutional, Full or part-time Employment: Portuguese Navy; Financial Interests, Institutional, Research Grant: Cuf Oncology, AstraZeneca; Financial Interests, Institutional, Advisory Role: NTT DATA; Financial Interests, Institutional, Principal Investigator: Gilead, Merck Sharp & Dohme, Nanobiotix; Financial Interests, Institutional, Invited Speaker: Merck KGaA, Nestlé, Pfizer, Uriage, Novartis. All other authors have declared no conflicts of interest.