INTRODUCTION and OBJECTIVES: Known for its ability to activate blood coagulation, Tissue Factor (TF) is also known to induces an intracellular signaling pathway initiated by the activation of the protease-activated receptor 2 (PAR-2) and leading to production of interleukin 8 (IL-8) in several non-tumoral and tumor cells. Detected at the membrane of different types of cancer cells, TF expression positively correlates to tumor aggressiveness and poor prognosis. Since IL-8 has been described to contribute to several aspects of tumor progression, we mean to investigate the role of IL-8 in TF-mediated tumor progression. MATERIAL and METHODS: We used a high-TF-expressing human breast cancer cell line as an aggressive mesenchymal basal-like model known to secrete high IL-8 (MDA-MB-231 TF-WT), as well as a Cas9 Crispr-established TF-silenced counterpart cell line (MDA-MB-231 TF-KO). RESULTS and CONCLUSION: We first analyzed the capacity of soluble factors obtained from both MDA-MB-231 TF-WT and TF-KO cells to induce pro-tumoral features in different cell types known to contribute to breast tumor microenvironment. As we used conditioned medium (CM) obtained from MDA-MB-231 TF-WT cells (CM-MDA-TF-WT) to treat poorly aggressive MCF7 tumor cells, we observed rapid and drastic alterations of its cellular morphology compatible to the loss of epithelial features, as well as significant increase of its migration ability (>4-fold) and CXCL8 gene expression (>15-fold). When treated with CM-MDA-TF-KO, MCF7 cells only showed poor increase of its migration ability and no significant stimulation of CXCL8 gene expression. We then observed CM-MDA-MB-231 effect on human neutrophils isolated from blood of healthy donors and showed that CM-MDA-TF-WT has higher capacity to chemo-attract when compared to CM-MDA-TF-KO. In a second step of the project, RT-qPCR and ELISA assays allowed us to confirm that the silencing of TF (MDA-MB-TF-KO) drastically inhibits CXCL8 expression and subsequent production of IL-8. Analysis of human mammary tumors expression data from The Cancer Genome Atlas (TCGA) allowed us to confirm that the CXCL8 gene is highly expressed in the most aggressive subtypes of human breast cancer and revealed a positive correlation between F3 (TF) and CXCL8 genes (IL-8) expression. Expression of both genes also positively correlate with the expression of a set of genes that identify neutrophils presence in tumor masses. Altogether, our results suggest that the presence of tumor cells with high levels of TF may contribute, through secretions in the microenvironment, to the progression of the tumor mass, possibly providing high IL-8 levels in the tumor microenvironment.