Abstract Background: Inflammation contributes to the increased invasiveness and poor prognosis in breast cancer (BC) patients. Specifically, the expression of the proinflammatory cytokines interleukin-6 (IL-6), tumor necrosis factor alpha (TNFα) and interleukin-1 (IL-1) have all been linked to increased invasiveness and poor prognosis. Interestingly, the increased invasiveness was associated with an increase in the acquisition of markers of epithelial-mesenchymal transition (EMT). Therefore, we determined whether the levels of circulating proinflammatory cytokines (IL-1, IL-6, TNFα) and antiinflammatory cytokines (IL10) were correlated with the induction of EMT transcription factors (TFs), Snail1, Zeb1, Twist1, in breast cancer patients. Materials and Methods: From two laboratory-based ongoing studies at the MD Anderson Cancer Center, 41 BC patients were assessed for EMT-TFs in circulating CD45-ve cells (EMT-CTCs) and for serum proinflammatory cytokines before starting any treatment. 32 of 41 patients assessed for EMT had metastatic BC. EMT-CTCs were detected by qRT-PCR for the EMT-TFs Snail1, Zeb1 and Twist1 (Mego 2011; PMID 21387303) and serum cytokines were measured by Luminex bead array assay (MILLIPLEX™ MAP Human Cytokine/Chemokine Panel). Cytokine serum concentrations were compared with the median cytokine levels of healthy donors (HD). We examined the association of serum cytokines above the median HD levels and the presence of EMT-CTCs by non-parametric Mann-Whitney test with a statistical significance for p<.05. Results: Of the 41 patients assessed for both serum cytokines and EMT-CTCs, 14 (34%) were positive for at least one EMT-TF, including 3 of 9 (33%) patients with no-metastatic BC and 11 of 32 (34%) patients with metastatic BC. We found that serum levels of IL1a, IL2, TGFα, and TNFβ in patients that were above the median levels of HD sera were higher in patients with EMT-CTCs in the blood (higher IL1a concentration in patients with over expression of Snail1, Zeb1, and Twist1; IL2 with Zeb1; TGFα with Snail1; TNFβ with Zeb1, and Twist1). Further, the higher ratio of proinflammatory/anti-inflammatory cytokines, was associated with the presence of at least one EMT-TF, e.g., IL8/IL10 (p=.005) and TNFα/IL10 (p=.037). Discussion: Patients with proinflammatory cytokine (IL1a, IL2, TGFα, and TNFβ) levels above the median levels of HD or who had a predominantly proinflammatory cytokine profile were more likely to have at least one EMT-TF in their blood. These data are consistent with the hypothesis that proinflammatory cytokines promote EMT, which may be involved in tumor aggressiveness and disease progression. Citation Information: Cancer Res 2011;71(24 Suppl):Abstract nr P1-02-07.