ABSTRACT
This chapter examines the nature of cancer by describing the natural history of the disease from a cellular standpoint. It discusses the molecular changes that make a cell cancerous. The chapter also discusses the development of cancer as a microevolution- ary process. Cancer cells break the most basic rules of cell behavior by which multicellular organisms are built and maintained, and they exploit every kind of opportunity to do so. The effort to combat cancer has led to many fundamental discoveries in cell biology. Cancers are classified according to the tissue and cell type from which they arise. Carcinomas are cancers arising from epithelial cells, and they are by far the most common cancers in humans. Most cancers have characteristics that reflect their origin. Skin cancers other than melanomas are not included in these figures, since almost all are cured easily and many are unrecorded.
