Background: Checkpoint proteins regulate the immune system. Breast cancer (BC) cells can up-regulate or down-regulate these proteins to evade anti-tumor immune responses. Soluble forms of immune checkpoint molecules (ICMs) can be measured in human plasma. The study aimed to measure the systemic levels of a series of co-stimulatory and co-inhibitory ICMs at diagnosis, post-neo-adjuvant chemotherapy (NAC) and post-surgery in newly- diagnosed BC patients (pts) relative to those of a healthy control group. Methods: Soluble ICMs were measured using multiplex bead array technology in plasma from 72 BC pts and 45 healthy controls. Data was prospectively obtained and levels compared between pre-treatment, post-NAC, and post-surgery using non-parametric tests (Mann-Whitney & Kruskal-Wallis). Results: Pre-treatment levels of the soluble stimulatory molecules viz. GITR (p<0.0001), GITRL (p< 0.020), CD27 (p< 0.024), CD40 (p< 0.021), ICOS (p< 0.009), as well as the inhibitory molecules PD-L1 (p< 0.0001), CTLA-4 (p< 0.005), TIM-3 (p< 0.0004), HVEM (p< 0.0004) were significantly lower in early BC pts compared to controls. Post-treatment, there were significant increases in most ICM levels (Table), with the exception of CTLA-4, which decreased significantly following treatment. On the other hand, pre-treatment plasma concentrations of CCL5 (RANTES) (84.22 vs. 48.72 pg/mL, p<0.0001), M-CSF (84.41 vs 13.34 pg/mL, p<0.0001), FGF-21 (24.36 vs. 8.64 pg/mL, p<0.001) and GDF-15 (806.82 vs. 430.03 pg/mL, p<0.0001) were significantly increased in the breast cancer pts compared to healthy controls. A pathological complete response (pCR) was documented in 65% of pts (mostly TNBC). There were no correlations between pre-treatment ICM levels, CCL5, M-CSF, FGF-21 and GDF-15 and pCR. Conclusions: We identified low levels of stimulatory and inhibitory ICMs in newly-diagnosed, non-metastatic BC pts compared to healthy controls. Following treatment, with the exception of CTLA-4, most of these pre-treatment abnormalities of systemic ICM levels corrected. NAC is associated with upregulation of sPD-L1 and most other ICMs. These results indicate that early BC is associated with down-regulation of soluble stimulatory and inhibitory ICMs. Newly-diagnosed early BC pts appear to have generalized immune-suppression independent of subtype and stage. To our knowledge, this is the first study to describe the effect of treatment on systemic ICMs in early BC pts.