Cancer genetics

Cancer is a genetic disease of somatic cells. Tumor karyotypes are rarely normal, and most show multiple abnormalities of both number and structure. The first direct evidence for this concept of cancer came from studies of tumor-specific translocations in leukemias and lymphomas, revealing the importance of oncogenes and the regulation of gene transcription in cancer. A second major source of information about human cancer genes is hereditary cancer. Genetic predisposition of the autosomal dominant type imposes a high relative risk for one or more kinds of cancer. In the past decade or so, more than 30 mutant genes for such hereditary cancers have been cloned. Penetrance depends upon additional, somatic, mutations. A few of the genes are oncogenes or DNA repair genes, but most are tumor suppressor genes. Some tumor suppressors regulate transcription, while others operate in signal transduction pathways that are involved in regulating processes of cell birth, differentiation, and death. The knowledge gained is stimulating new approaches to the treatment and prevention of cancer.