Cancer is a disease of genes gone awry.
Genes that control the orderly replication of cells become damaged, allowing the cell to reproduce without restraint and eventually to spread into neighboring tissues and set up growths throughout the body. All cancer is genetic, in that it is triggered by altered genes. Most cancers come from random mutations that develop in body cells during one's lifetime - either as a mistake when cells are going through cell division or in response to injuries from environmental agents such as radiation or chemicals. Cancer usually arises in a single cell. The cell's progress from normal to malignant to metastatic appears to follow a series of distinct steps, each one controlled by a different gene or set of genes.