It is as if there is a piano in each cell, with only certain keys allowed to play in different cell types. If several suppressor genes are lost or damaged, the cell may begin unregulated cell growth. It is this unregulated growth that we call cancer. These changes occur in a single cell after conception, and need not occur in the order shown. Mutations in the BRCA1 and BRCA2 genes are examples of strong hereditary factors.
All cancers are due to changes in the genes.
Cancers that are not due to hereditary factors are brought about by changes in somatic cell genes that occur after conception. Cancers due to strong hereditary factors result from a change in at least one gene in an egg or sperm cell that occurs before conception, and at least one change in the genes of a somatic cell that occurs after conception. Only a genetic change that occurs in an egg or a sperm cell can be passed from one generation to another. An increased hereditary susceptibility to breast and ovarian cancer can be passed through the father's as well as the mother's side of the family. For this reason, both sides of an individual's family must be analyzed.