Sialoadhesin, a macrophage restricted adhesion molecule frequently expressed in macrophages infiltrating breast tumors, binds to sialic acid on MUC1 expressed by the breast cancer cell line MCF-7 [119], an interaction that may be of importance not only for macrophage infiltration of tumors, reputed to be a source of cytokines and angiogenic factors which promote tumor growth, but also, paradoxically, to enable tumor cell killing by macrophages [120]. Here, MUC1 is linked to breast cancer.