Cellular interactions in the metastatic process.

Tumor metastasis is a multistep process which is dependent on both host and tumor properties. It is proposed that the interaction of normal host blood and endothelial cells with circulating malignant cells result in tumor cell arrest leading to subsequent metastases at specific secondary sites. In experimental animal models the frequency and location of metastatic foci can be manipulated by repeated in vivo selection for tumor cell variants showing altered preference for organ-specific implantation and survival. These tumor cell variants can be used to determine the cell surface structures and enzymes involved in the various steps of the metastatic process.