Immune microenvironment of cancer bone metastasis

Bone is a common and frequent site of metastasis in cancer patients, leading to a significant reduction in quality of life and increased mortality. Bone marrow, the primary site of hematopoiesis, also serves as both a primary and secondary lymphoid organ. It harbors and supports a diverse array of immune cells, thereby creating a distinct immune microenvironment. These immune cells engage in a range of activities, including anti-tumor, pro-tumor, or a combination of both, which influence the development and progression of bone metastases. Rapid advances in cancer immunotherapy have underscored its potential to eradicate bone metastases. However, clinical outcomes have not yet met expectations. To improve the efficacy of immunotherapy, it is crucial to gain a comprehensive and in-depth understanding of the immune microenvironment within bone metastases. This review provides an overview of the current understanding of the role of different immune cells, their anti-tumor and pro-tumor activities, and their overall contribution to bone metastasis.