Independently of tumour and treatment modulation, the host immune response status plays an important role in the clinical outcome of patients with cancer. The influence of single nucleotide polymorphisms (SNPs) and adjuvant radiotherapy (RT) on the systemic immune response status of patients with breast cancer was investigated. Materials and Methods: Eighty-six female patients recovering from breast cancer surgery were investigated. As a control cohort, 82 healthy female blood donors were used. Blood-based SNPs, plasma C-reactive protein (CRP), cytokines and chemokines were analyzed for this purpose. Results: Independently of tumour stage and hormone receptor status, dysregulation of plasma CRP, chemokine (C-C motif) ligand 4 (CCL4) and interleukin 2 (IL2), but not CCL5, CCL2, platelet-derived growth factor, IL6, IL10, IL12, interferon-gamma or tumour necrosis factor alpha were detected in the patients when compared to controls. The extent of alteration in plasma levels of CRP and IL2 patients was significantly associated with SNPs in CRP rs1800947 and IL2 rs6822844, respectively. These SNPs had no influence on the levels of corresponding plasma biomarkers in the healthy controls. Adjuvant RT reduced plasma CRP and CCL5 levels in patients with regards to CRP rs1800947CC, CCL5 rs2107538GG and CCL5 rs2280789AA sequences. Conclusion: Dysregulation of immune responses, as indicated by plasma levels of CRP, CCL4 and IL2 were found in patients with breast cancer despite the removal of the tumour mass. The benefit of adjuvant RT, as indicated by reduced plasma amounts of inflammatory protein CRP and chemokine CCL5 were based on the SNPs of the patients. Analyses of blood-based SNPs, plasma CRP, IL2 and CCL5 are low cost, rapid and can be carried out using general laboratory facilities while requiring only a peripheral blood sample. The possibility of using these blood-based biomarkers as an indicator of patient immune status for selection of individual patient treatment warrants further investigation.