Beyond the tumor: the role of the gut microbiome in triple-negative breast cancer.

The gut microbiome, a metabolically active community of microorganisms in the gastrointestinal tract, regulates host immunity, metabolism, and inflammation. Dysbiosis, or disruption of this ecosystem, has been linked to cancer initiation, progression, and therapy resistance. Triple-negative breast cancer (TNBC) accounts for 10-15% of breast cancers and is managed primarily with chemotherapy and immune checkpoint inhibitors; however, treatment responses remain variable and these patients are at higher risk of cancer recurrence compared to patients with hormone receptor-positive or HER2-positive breast cancer. Emerging evidence suggests that the gut microbial composition and its diversity can influence outcomes and therapeutic efficacy of systemic treatments in TNBC. We review the current epidemiologic, mechanistic, and clinical evidence on how the gut microbiome influences TNBC biology, with particular attention to the tumor immune microenvironment and response to therapy. We highlight protective and pro-tumorigenic microbial signatures, the impact of antibiotics and obesity, and emerging strategies, such as dietary modulation and microbiome-targeted interventions, that may ultimately be used to optimize TNBC management and improve patient outcomes.