Mutation and Cancer

Abstract

It is now clear that cancer is a genetic disease. Cancer has many causes, but ultimately all these causes exert their effects on a special class of genes called cancer genes or proto-oncogenes. Many of these proto-oncogenes have now been identified and mapped, as shown in Figure 15-26. Oncogenes normally carry out basic cellular functions, generally related to the regulation of cell division. However, several types of events can change a proto-oncogene into an oncogene\textemdash that is, into a state in which it promotes the two main characteristics of cancer: (1) uncontrolled cell division leading to an overgrown group of cells called a tumor and (2) the spread of tumor cells throughout the body to form new tumors, a process called metastasis. One of the main ways in which proto-oncogenes can be changed into their cancer-causing (oncogenic) state is by mutation. Spontaneous or environmentally induced mutation occurs in a proto-oncogene of a single cell, which then undergoes multiple cell divisions to form a tumor. Because all the cells of the tumor carry the mutated oncogene, you can see that a tumor is a mutant clone. This, then, is the sense in which cancer is a genetic disease caused by somatic mutation.Figure 15-26Human chromosomes showing bands from Giemsa staining and the positions (shown by black dots) of known proto-oncogenes; mutations in proto-oncogenes lead to cancer.