Tumor cell progression and differentiation in metastasis.

The development and evolution of tumors is regulated by both genetic and epigenetic events. It is thought that these processes tend to drive neoplastic development in opposing directions so that tumor progression, predominantly as a consequence of mutational events, leads to increasing tumor aggression. Conversely the induction of differentiation, largely through epigenetic mechanisms, tends to cause tumors to evolve to a more benign phenotype. However, these generalizations are a simplistic view of a complex dynamic event where both processes can be overlaid within a single neoplasm. Using malignant melanoma as a model system the alterations in gene expression and their effects upon metastatic dissemination, that accompany some of these changes, both natural and induced, are described.