A genetic basis for metastasis

The progression of a normal cell to one that is malignant is characterized by at least four progressive but potentially separable behavioural patterns identifying the immortal, tumorigenic, invasive and metastatic phenotypes. A multitude of steps appear to be involved in both transformation from normality and progression to malignancy as characterized by the acquisition of metastatic behaviour. Consequently, it seems unlikely that a single gene can directly manifest expression of the metastatic phenotype in normal cells unless it can induced pleiotropic effects. Indeed, a single trait uniquely characterizing the metastatic phenotype has never been identified. The possibility of a single gene suppressing the metastatic phenotype seems much greater. One possible candidate for such a gene is nm23, the expression of which correlates with reduced metastatic potential in several tumours including breast cancer in humans. Although the numbers involved are still small, the correlation of nm23 expression with breast cancer outcome offers potential in using this system as a prognostic aid in clinical diagnosis of this disease. Its possible role as an indicator of metastatic potential in other human tumours remains to be evaluated, although current evidence suggests that it is unlikely to be of use in colon cancer. Further significant progress requires molecular dissection of the mode of action of its product.