Techniques for inhibiting tumor metastases.

Of the four major biological mechanisms of cancer spread, hematogenous dissemination is perhaps the most significant, as it usually heralds a fatal outcome for the patient. Recent experimental approaches have shown ways of altering the metastatic process and even totally inhibiting it in some animal models. It appears that these models may be applicable to certain human cancers. To prevent hematogenous metastasis formation the process must be inhibited at any one of four levels: 1) growth of the primary; 2) invasion of vessel walls; 3) release of viable tumor cells; or 4) entrapment and growth in distant organs. Judicious handling of the primary can decrease metastasis by minimizing the shedding of tumor cells. New experimental agents prevent the release of tumor cells from the primary by normalizing the blood vessels of the tumor. Warfarin, heparin, and fibrinolytic agents inhibit the entrapment of circulating tumor cells, presumably by their effect on coagulative mechanisms. A better understanding of the benefits of combined approaches to cancer using chemotherapy, irradiation, and immunotherapy, alone and as adjuncts to surgery, offers new opportunity to study methods of controlling metastatic disease.