Background: Toll-like receptor 4 (TLR4) and phosphorylated signal transducer and activator of transcription protein 3 (pSTAT3) hold a key role in inflammatory response and tumor immune evasion. Their role in the peripheral immune response and in tumor immune interactions in circulation needs further investigation. In the current report we evaluated the incidence of TLR4 and pSTAT3 expression on tumor and immune compartments within the peripheral blood (PB) of patients with early (eBC) and metastatic breast cancer (mBC). Methods: PB was obtained from patients with eBC (n = 99) and mBC (n = 100), prior to adjuvant and first-line therapy, respectively. Triple immunofluorescence staining for cytokeratins (CK), TLR4 and pSTAT3 was performed on peripheral blood mononuclear cell (PBMC) cytospins. Single cell-level expression of TLR4 and pSTAT3 was assessed on CK+ circulating tumor cells (CTCs) and PBMCs using the Ariol microscopy system. Results: CK+ CTCs were detected in 6.1% and 19% of patients with eBC and mBC, respectively (p = 0.006) (number of CTCs: n = 34 and n = 28, respectively). Higher TLR4 expression rates on CTCs were observed in mBC as compared to eBC (53.6% vs 7.7% of CTCs, 13% vs 3% of patients; p = 0.016). pSTAT3+ CTCs also prevailed in mBC (60.7% vs 10.3% of CTCs; 14% vs 5.1% of patients; p = 0.032). In the metastatic patients, CTC detection was associated with shorter overall survival (median OS: 24.9 vs 36.5 months; p = 0.042; Kaplan Meier), whereas the detection of TLR4+ CTCs predicted for shorter progression free survival (median PFS: 11.4 vs 12.6 months; p = 0.036). At the PBMC level, TLR4 expression was more frequent among patients with mBC as compared to eBC (34% vs 20.2%, respectively; p = 0.029), whereas pSTAT3 expression prevailed in eBC (89.9% vs 77% of patients, respectively; p = 0.014). The detection of TLR4+ PBMCs was associated with reduced disease-free survival (median DFS: not reached; p = 0.007) and shorter OS (median OS: not reached; p = 0.028) in patients with eBC. Conclusions: TLR4 and pSTAT3 expression is demonstrated on CTCs and PBMCs and significantly varies among eBC and mBC, suggesting that the inflammatory signaling through TLR4 and pSTAT3 in PB could be associated with BC progression. Our results further imply that their assessment in PB may hold significant prognostic implications in BC.