Genetics, Epigenetics and Cancer

Abstract

With deeper understanding of cell biology and genetics, it now appears that cancer is less an organ disease and more a disease of molecular mechanisms caused by mutations of specific genes. Cancer is fundamentally a disease of tissue growth regulation failure when the genes that regulate cell growth and differentiation are altered. Most cancers have multiple possible concurring causes, and it is not possible to prevent all such causes. However, only a small minority of cancers (5-10%) are due to inherited genetic mutations whereas the vast majority (90-95%) are non-hereditary epigenetic mutations that are caused by various agents (environmental factors, physical factors, and hormones). Thus, although there are some genetic predispositions in a small fraction of cancers, the major fraction is due to a set of new genetic mutations (called "epigenetic" mutations). After a brief primer on cancer and its genetics, this article focuses on the epigenetics of cancer. Epigenetics is the study of cellular and physiological traits inherited by daughter cells, but not caused by changes in the DNA sequence. Important examples of epigenetic mechanisms (DNA methylation, histone modification, chromatin remodeling) and agents (prions, RNA and miRNA) are discussed. Epigenetic evidence in humans and epigenetic inheritance are reviewed to include environmental exposure, genomic imprinting and trans-generational inheritance. Epigenetic carcinogens and cancer treatment are also treated.