Changes in intestinal microbiota in postmenopausal oestrogen receptor positive breast cancer patients treated with (neo)adjuvant chemotherapy

Previous pre-clinical research has indicated that the intestinal microbiota can potentiate anti-tumour efficacy of chemotherapy and that chemotherapy can affect intestinal microbiota. Using a longitudinal design, this clinical study explored the associations between the intestinal microbiota, chemotherapy toxicity, and treatment response in postmenopausal oestrogen receptor positive breast cancer patients. Forty-four postmenopausal breast cancer patients with oestrogen receptor positive breast cancer were prospectively enrolled in a multicentre cohort study and treated with 4 cycles of (neo)adjuvant adriamycin, cyclophosphamide (AC) followed by 4 cycles of docetaxel (D). Patients collected a faecal sample and completed a questionnaire before treatment, during AC, during D, and after completing AC-D. Intestinal microbiota was analysed by amplicon sequencing of the 16S rRNA V4 gene-region. In the whole group, observed species richness reduced during treatment (p=0.042). The abundance of Proteobacteria, unclassified Enterobacterales, Lactobacillus, Ruminococcaceae NK4A214 group, Marvinbryantia, Christensenellaceae R7 group, and Ruminococcaceae UCG-005 changed significantly over time. Patients with any grade diarrhoea during docetaxel treatment had a significantly lower observed species richness compared to patients without diarrhoea. In the small group of neoadjuvant treated patients (N=18), pathologic response was unrelated to baseline intestinal microbiota richness, diversity and composition.