In this paper, we will review the data on stromal components and immunological parameters in the cancer microenvironment as prognostic and predictive markers in
breast cancer. Host immunological response to
cancer has gained importance because of recent breakthroughs in
immunotherapy. Currently, molecular and clinical subtyping of
breast cancer is solely based on the molecular features of the
cancer cells without considering the importance of stromal components. There is now clear evidence that infiltrating immune and inflammatory cells influence the biology and
clinical course of
breast cancer. However, the prognostic and predictive function of immune cells differs between
breast cancer subtypes. Immune parameters are established and validated prognostic and predictive markers in triple negative and for HER2 positive breast
cancers and may be ready to be used as stratification parameters in clinical trials and as adjunct variables when making clinical decisions. On the other hand, the prognostic and predictive impact is minimal in low grade,
luminal A type breast
cancers. The strong association between higher lymphocytic infiltration and better outcome (including greater
chemotherapy sensitivity) in TNBC and HER2 positive
cancers also raises novel therapeutic options that target immune cells to increase their activity.
Immune markers also carry the potential to serve as predictive markers to select patients for immunotherapeutic regimens (e.g. checkpoint inhibitors).