Abstract
Chemotherapy frequently causes debilitating gastrointestinal symptoms, which are inadequately managed by current treatments. Recent research indicates the gut microbiome plays a role in the pathogenesis of these symptoms. The current study aimed to identify pre-chemotherapy microbiome markers that predict gastrointestinal symptom severity after breast cancer chemotherapy. Fecal samples, blood, and gastrointestinal symptom scores were collected from 59 breast cancer patients before, during, and after chemotherapy. Lower pre-chemotherapy microbiome alpha diversity and abundance of specific microbes (e.g., Faecalibacterium) predicted greater chemotherapy-induced gastrointestinal symptoms. Notably, tumor and diet characteristics were associated with lower pre-chemotherapy alpha diversity. Lower baseline alpha diversity also predicted higher chemotherapy-induced microbiome disruption, which was positively associated with diarrhea symptoms. The results indicate certain cancer patients have lower microbiome diversity before chemotherapy, which is predictive of greater chemotherapy-induced gastrointestinal symptoms and a less resilient microbiome. These patients may be strong candidates for pre-chemotherapy microbiome-directed preventative interventions (e.g., diet change).