Significance of Tumor Microenvironment Scoring and Immune Biomarkers in Patient Stratification and Cancer Outcomes

Tumors appear as heterogeneous tissues that consist of tumor cells surrounding by a tumor microenvironment (TME). TME is a complex network composed of extracellular matrix (ECM), stromal cells, and immune/inflammatory cells that drive cancer cells fate from invasion to intravasation and metastasis. The stromal-inflammatory interface represents a dynamic space, in which exchange of numerous molecular information is associated with the transition into tumorigenic microenvironment. Recruitment, activation, and reprogramming of stromal and immune/inflammatory cells in the extracellular space are the consequences of a reciprocal interaction between TME and cancer cells. Recent data suggest that cancer development is influenced by TME and controlled by the host’s immune system, underlying the importance of TME components and immune biomarkers in the determination of prognosis and response to therapy. The immune classification has prognostic value and may be a useful supplement to the histopathological, molecular, and TNM classifications. Nevertheless, the complexity of quantitative immunohistochemistry and the variable assay protocols, stromal and immune cell types analyzed underscore the need to harmonize the quantified methods. It is therefore important to incorporate TME and immune scoring in determinations of cancer prognosis and to make sure they become a routine part of the histopathological diagnostic and prognostic assessment of patients.