Exploring the human breast cancer intra-tumor microbiome and its clinical significance

Growing evidence implicate intra-tumor bacteria in cancer progression and response to therapy. Our recent findings demonstrated that the microbiome of breast tumors is exceptionally rich and diverse. However, its clinical significance is largely unknown. In this study, we aim to explore the impact of intra-tumor bacteria and their metabolic function on the clinico-pathological features of breast cancer and on response to therapy.

To investigate the associations between clinical parameters and intra-tumor bacteria, we gathered comprehensive medical information for 145 primary breast cancer patients whose tumors were sequenced for bacterial DNA. To study the relationship with anti-cancer treatment, we collected pre-treatment tumors from 67 patients, ranging in response to neoadjuvant chemotherapy – plus 44 matched post-treatment samples. We extracted bacterial DNA from their tumors, and identified bacterial species and annotated functions using bioinformatics tools.

Preliminary analysis significantly associates clinical parameters with intra-tumor bacteria and their functions. For example, specific bacterial taxa or functions correlate with estrogen receptor status, lymph node involvement, smoking history and menopausal status. Furthermore, pre-treatment microbiomes significantly differentiate between responders and non-responders to chemotherapy. Importantly, post-treatment samples exhibit distinct and unexpectedly enriched microbiomes compared to pre-treatment samples.

Our findings correlate intra-tumor bacteria with clinical features and treatment outcome in breast cancer. Further studies are underway to reveal their functional role. Analyzing the altering bacterial populations within breast tumors, in association with clinico-pathological parameters, will promote our understanding of their role in breast carcinogenesis, and may offer novel approaches for diagnostics, prevention and therapy.