Macrophages and cancer metastasis.

Activated macrophages appear to be able to recognize and destroy neoplastic cells without regard to their phenotypic diversity, and macrophage-mediated cytotoxicity appears invulnerable to the problem of cellular resistance to killing which is routinely encountered in efforts to destroy tumor cells by cytotoxic drugs. However, macrophage-mediated destruction of large tumor burdens may not be feasible. In many tumors the number of macrophages is too low to destroy all tumor cells, even if the macrophages are activated to the optimal tumoricidal state. For this reason, systemically administered immunomodulators encapsulated in liposomes should be used to activate macrophages to destroy those few tumor cells resistant to other means of therapy.