Hi. Cancer is a genetic disease, but the genetic defect (mutation) lies in those genes which regulate the growth, development and life span of normal cells in the body. The body has two kinds of cells: somatic cells (the usual cells in a patient's body) and germ cells (sperm and egg cells, which serve to pass on the parents' genetic material to the children). If the mutation in the regulatory genes affect only the somatic cells, then the cancer which develops will not be passed on to the offspring. But if the mutation affects the genes in the germ cells as well, then the potential for developing cancer may be inherited by the children. Examples of hereditary cancer conditions include the BRCA 1 and 2 breast cancer genes, and hereditary polyposis in colon cancer.