We have described a number of phenotypic and genotypic differences between defined tumor sublines from the Eb/ESb model system that differ greatly in metastatic capacity. Some of these differences are summarized in Figure 5. It can be seen that the differences are both structural and functional. They include differences in the glycosylation of membrane glycoproteins as well as differences in total membrane protein composition. The functional differences refer particularly to enzymatic activities, cell motility, and invasive capacity. In addition, a change in membrane fluidity and membrane dynamics was seen when we investigated membrane vesicles shed spontaneously from these tumor lines. ESb type cells were found to shed about three times as much membrane material as the low-metastatic, Eb cells. Since such vesicles carried degradative enzyme activity, they could play a role in the invasion process. The vesicles also carried TATA and thus could also play a role in preventing immunological attack against these tumor cells. Another immunological escape mechanism was found to be based on the ability of the high-metastatic cells to generate immunoresistant variants that no longer expressed the respective TATA. A cytogenetic comparison of such immunoresistant variants with the TATA+ line revealed several chromosomal changes. The contribution of chromosomal rearrangements to the ability of malignant cells to generate variants was discussed.