Etiology of Cancer

Abstract

Cancer is a pathologic accumulation of clonally expanded cells derived from a common precursor. The fundamental cause of all cancers is genetic damage that is usually acquired but is sometimes congenital. In general, the genetic dysregulation that gives rise to uncontrolled cell proliferation results from either activation of growth-promoting oncogenes and/or deletion/inactivation of growth-inhibiting tumor suppressor genes. Additional contributions to carcinogenesis come from genes that regulate programmed cell death (apoptosis) and genes involved in DNA repair. The most widely accepted theory of cancer development is the Knudson “2-hit” hypothesis, which posits that a mutation in one predisposing gene is necessary but not sufficient for malignancy and that only after development of a second mutation will invasive cancer develop. In this chapter, we discuss the major categories of carcinogens and their role in the etiology of cancers with emphasis on common ophthalmic cancers.