The breast tumor microenvironment: role in cancer development, progression and response to therapy.

INTRODUCTION: Numerous clinical and pre-clinical studies have provided ample evidence supporting that the tumor microenvironment plays a significant role during breast cancer development, progression and in determining the therapeutic response. Areas covered: This review focuses on the evolving concept of the microenvironment as the critical participant in each step of the multi-stage process of malignant progression. Currently, only a small number of molecules form part of routine molecular diagnostics in breast caner, but microenvironment-derived biomarkers are potential additions to existing predictive and prognostic marker panels. The authors discuss the dependency of the breast tumor cells on different components of the microenvironment for their survival, dissemination, dormancy and establishment in secondary sites to form overt metastasis, as well as the potential as a therapeutic target to improve breast cancer outcome. Expert commentary: Despite the importance in the development of breast cancer, the contribution of the microenvironment is not considered in routine diagnostic testing or informing therapeutic decisions. However, introduction of immunotherapy will increasingly require patient selection based on the stromal composition of the primary breast tumor. Better understanding of the role of specific microenvironment-derived molecules is likely to inform personalized therapy, leading to improved patient outcome.