ABSTRACT
Uncontrolled proliferation constitutes a central problem in tumor biology. Growth of malignant cells in vivo and in vitro often occurs independently from exogenous stimulators, and is unresponsive to regulatory signals. In contrast, proliferation of normal cells during embryological development, self-renewal, or tissue repair is contained, and apparently subject to homeostatic regulation. Growth control of normal cells depends on external signals which have mitogenic or growth inhibitory effects on target cells. The majority of physiological growth regulatory molecules are polypeptides which bind specifically to membrane receptors and act in a hormone-like fashion. Continuous monitoring of karyotypic abnormalities in serially passaged melanoma cell lines reveals a strikingly stable distribution of marker chromosomes, and does not indicate any selection of subpopulations during routine culture. Human malignant melanoma provides one of the best characterized systems to study aberrant growth regulation in a spontaneously occurring human neoplasm.
