Macrophage therapy of cancer metastasis.

The biological heterogeneity of metastatic neoplasms and the production of metastases that are resistant to therapy is the major cause of death from cancer. The successful therapy of disseminated metastases must therefore circumvent the problems of neoplastic heterogeneity and the development of resistance to therapy by tumour cells. Macrophages can be activated in situ by interaction with liposomes containing various immunomodulators. Repeated administration of such liposomes has eradicated cancer metastases in several tumour systems. Macrophage destruction of cancer metastases is limited by the ratio of effector to target cells. Thus, destruction of small metastases is effective but once metastases exceed a certain number of cells the therapeutic efficacy is diminished. For this reason we have been investigating various methods of reducing the tumour burden in metastases by modalities such as chemotherapy or radiotherapy and of using tumoricidal macrophages to treat the few tumour cells that escape destruction by conventional therapeutics.