Cancer is an uncontrolled division of abnormal cells. In most cases, the exact cause of cancer is not known. DNA is the 'blueprint' for life, the set of instructions carried in the nucleus of every cell. A discrete unit of instruction contained in the DNA is called a gene.
Tumor suppressor genes block cell division, or instruct cells to die when appropriate.
Even when cancer-related mutations are present in a cell, cancer does not always develop. The reason for this is not known. The majority of all cases of cancer, however, are related to acquired mutation. Each time a body cell divides, the DNA must be replicated, so that each daughter cell receives a complete copy of the genetic material. Mistakes can and do occur during the DNA replication process.