A. Apoptosis and the Genesis of Tumors

Malignant cancers arise as the culmination of a multistage process, and passage through this process may be characterized genetically, morphologically, or bio­ logically. Genetically, tumors are distinguished from normal tissue by alter­ ations in the structure and/or expression of multiple genes, including particular oncogenes and tumor suppressor genes (PONDER 2001).Associated phenotypic change is indicated by the appearance of hyperplastic, ben ign, invasive, and finally metastatic cell populations, it being recognized that each of these terms is indicative of a spectrum of morphological changes . In terms of biological change, HANAHAN and WEINBERG (HANAHAN and WEINBERG 2000) have sug­ gested that tumors differ from normal tissue by their self-sufficiency in growth signals, resistance to antigrowth signals, evasion of apoptosis, limitle ss replica­ tive potential, sustained angiogenesis, and tissue invasion and metastasis. Each of thes e characteristics may be traced back to particular, and not necessarily