The tumors of especially aggressive forms of estrogen negative (ER-) breast cancer are more likely to contain cytokines than are less aggressive forms of breast cancer. Cytokines are small proteins that influence cells, causing them to act or inhibiting their function. They are released by the immune system. Specific types of cytokines, of IL-8, MCP-1 and MIP-1β, are especially important in the body’s defense against breast cancer.
Source: “Oestrogen receptor negative breast cancers exhibit high cytokine content,” Breast Cancer Research, January 2007.