The higher incidence of breast cancer in developed countries has been tempered by reductions in mortality, largely attributable to screening programs, improved surgery, and advances in preoperative and adjuvant systemic therapy. Decisions regarding use of systemic therapy in early breast cancer patients are mainly based on prognostic and predictive factors like lymph node status and tumor status regarding size, grade, and hormone receptor and HER2 expression . However, the currently used prognostic factors do not provide optimal risk-stratification. The goals of personalized medicine and targeted therapy demand further information regarding residual disease risk and potential benefit of additional treatments in specific circumstances. Therefore, additional prognostic and predictive information is sought in order to improve tailored treatment for patients with breast cancer. Understanding cancer biology gives further insight in factors influencing tumor control or progression and therefore might contribute in finding prognostic and predictive biomarkers. One of the cornerstones in cancer biology and an important factor in the outcome of tumor development is the interaction between the immune system and cancer cells, which, in case of tumor progression leads to tumor variants with an immune escape phenotype . In this interaction HLA-G is thought to be one of the key players.