Immunology of Solid Tumors Beyond Tumor-Infiltrating Lymphocytes: The Role of Tertiary Lymphoid Structures

Abstract

Immune cells and other constituents of the immune system make up an important part of the tumor microenvironment. Due to increased knowledge on the biology of the immune system in solid tumors and the successes with the treatment of patients with drugs that target its function, interest in immuno-oncology has increased enormously since the first successful trials. The first part of this chapter gives an overview of our current understanding of the role of the immune system in solid tumors, with a focus on the role of tumor-infiltrating lymphocytes (TILs) and their organization in structures called tertiary lymphoid structures (TLS). The increased interest in immuno-oncology has also triggered the search for predictive and prognostic biomarkers. One of the best characterized tissue-based biomarkers of the immune response in solid tumor is the presence of TILs. The second part of the chapter, which focuses on breast cancer, describes currently available data on TILs as a prognostic biomarker, challenges on the assessment of TILs, and TLS and the efforts of the International Immuno-Oncology Biomarker Working Group on standardization of its assessment.