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Cancer Res. 2019 May 7. pii: canres.3464.2018. doi: 10.1158/0008-5472.CAN-18-3464. [Epub ahead of print]

Pre-existing commensal dysbiosis is a host-intrinsic regulator of tissue inflammation and tumor cell dissemination in hormone receptor-positive breast cancer.

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Microbiology, Immunology, and Cancer Biology, University of Virginia.
Department of Cell Biology, University of Virginia.
School of Medicine, University of Virginia School of Medicine.
Microbiology, Immunology, and Cancer Biology, University of Virginia Medical Center.
Department of Pathology, University of Virginia Medical Center.
Biostatistics, Virginia Commonwealth University.
Department of Biostatistics, Virginia Commonwealth University Medical Center.
Department of Pathology, Virginia Commonwealth University.
Microbiology, Immunology, and Cancer Biology, University of Virginia Medical Center mr2ee@Virginia.EDU.


It is unknown why some patients with hormone receptor-positive (HR+) breast cancer present with more aggressive and invasive disease. Metastatic dissemination occurs early in disease and is facilitated by crosstalk between the tumor and tissue environment, suggesting that undefined host-intrinsic factors enhance early dissemination and the probability of developing metastatic disease. Here we have identified commensal dysbiosis as a host-intrinsic factor associated with metastatic dissemination. Using a mouse model of HR+ mammary cancer, we demonstrate that a pre-established disruption of commensal homeostasis results in enhanced circulating tumor cells and subsequent dissemination to the tumor-draining lymph nodes and lungs. Commensal dysbiosis promoted early inflammation within the mammary gland that was sustained during HR+ mammary tumor progression. Furthermore, dysbiosis enhanced fibrosis and collagen deposition both systemically and locally within the tumor microenvironment and induced significant myeloid infiltration into the mammary gland and breast tumor. These effects were recapitulated both by directly targeting gut microbes using non-absorbable antibiotics and by fecal microbiota transplantation of dysbiotic cecal contents, demonstrating the direct impact of gut dysbiosis on mammary tumor dissemination. This study identifies dysbiosis as a pre-existing, host-intrinsic regulator of tissue inflammation, myeloid recruitment, fibrosis, and dissemination of tumor cells in HR+ breast cancer.

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