Heterogeneity of monocytes in cancer

Monocytes, a crucial element of the innate immune system, act as the primary cells in the body's immune response. Approved by the International Federation for Immunology in 2010, monocytes are categorized into three subsets based on the degree of cell surface molecule expression: classical monocytes, intermediate monocytes, and non-classical monocytes. Generally, different monocyte subsets have diverse responsibilities and can mutually transform to maintain the stability of the internal environment. Distinctions in functional characteristics and associations with diseases have been identified among the various monocyte subsets. This review aims to describe the expression and functions of monocytes in detail and discuss their roles in cancer immunity, which offers a novel approach for the diagnosis, treatment, and prognosis of tumors by exploring and summarizing the distribution of monocyte subsets in tumors. By delving into the distribution and functional characteristics of different monocyte subsets in tumors, it holds the promise of guiding individualized therapies and more precise tumor management.