Development and prevention of metastasis.

Metastatic spread of malignancy is the primary cause of treatment failure and subsequent death in cancer patients. All cancers have the capability to metastasize, however, there are notable exceptions which rarely if ever metastasize. These include basal cell carcinoma, or cancers which are primarily locally invasive such as primary brain cancers. Is metastasis is an earlier process in cancer progression than originally hypothesized? Over 70% of patients have occult or overt metastatic disease at the time of presentation. Thus, the overwhelming proportion of patients have disease which is not surgically resectable for cure at the time of diagnosis. Metastasis is a continuous process commencing early in the growth of the primary tumor before it is clinically detectable by the most sensitive of means. In addition, metastases have the propensity to metastasize. The size and age variation in metastases, their dispersed anatomic locations, the local vascular and lymphatic environment, and their heterogeneous composition hinder complete surgical extirpation of disease and limit the effective concentration of anticancer drugs that can be delivered to metastatic colonies.