Immune response profile of primary tumour, sentinel and non-sentinel axillary lymph nodes related to metastasis in breast cancer: an immunohistochemical point of view

Approximately 1.67 million new cases of breast cancer (BC) are diagnosed annually, and patient survival significantly decreases when the disease metastasizes. The axillary lymph nodes (ALNs) are the main doorway for BC tumoral cell escape, through which cells can disseminate to distant organs. The immune response, which principally develops in the lymph nodes, is linked to cancer progression, and its efficacy at controlling tumoral growth is compromised during the disease. Immunohistochemistry (IHC) is one of the most widely used research techniques for studying the immune response. It allows the measurement of the expression of particular markers related to the immune populations. This review focuses on the role of the immune populations in the primary tumour in the locoregional metastasis of the ALN, and the relationship of the immune response in these regions to distant metastasis. We considered only studies of immune cells using IHC techniques. In particular, lymphocytes, macrophages and dendritic cells all play important roles in BC and have been extensively studied. Although further research is needed, there is much evidence of their role in the invasion of the ALN and distant organs. Their association with tumoral growth or protection has not yet been demonstrated decisively and is very likely to be determined by a combination of factors. Moreover, even though IHC is a widely used technique in cancer diagnosis and research, there is still room for improvement, since its quantification needs to be properly standardized.