The role of tumor infiltrating lymphocytes in development, progression and prognosis of non-small cell lung cancer

A malignant tumor is not merely an accumulation of neoplastic cells, but constitutes a microenvironment containing endothelial cells, fibroblasts, structural components and infiltrating immune cells which impact tumor development, invasion, metastasis and outcome. Hence, the evolution of cancers reflects intricate cellular and molecular interactions between tumor cells and constituents of the tumor microenvironment. Recent studies have shed new light on this complex interaction between tumor and host immune cells, and the resulting immune response. The composition of the immune microenvironment differs across patients as well as cancers of the same type, including various populations of T cells, B cells, dendritic cells, natural killer cells, myeloid-derived suppressor cells, neutrophils and macrophages. The type, density, location, and organization of immune cells within solid tumors define the immune contexture, which has proved to be a major determinant for tumor characteristics and patient outcome. Lung cancer constitutes mostly non-small cell lung cancer (85%), and is our most deadly malignant disease with 5-year survival being merely 15%. This review focuses on the immune contexture, the tumor-suppressing roles of tumor infiltrating lymphocytes, and how this immune contexture has relevance for cancer diagnostics, prognostication, and treatment allocation with an emphasis on NSCLC.