Family Cancers
Because cancer is so prevalent, many individuals have some family history of it. These histories can vary quite a bit. One person may have only an uncle with prostate cancer, whereas another may have a brother withbone cancer, a sister with breast cancer, and a father with lymphoma.
How do you know if your family medical history indicates that your family is especially prone to cancer? And to which cancers in particular?
A properly taken family cancer history, genetic counseling, and appropriate genetic testing can help determine if there is a strong, moderate, or low family and individual risk of cancer.
In trying to understand one’s risk of developing cancer it is important to note that most cancers affect us in a pattern that is called sporadic: they occur in individuals without an apparent family concentration of the same type of cancer. The reasons for sporadic cancer development have more to do with environmental influences and aging (cancer is more common in those over age sixty) than to an inherited, genetic predisposition to cancer. This is not to say that one’s family DNA is unimportant, because it is. What it does mean is that a single inherited abnormal gene is not the cause of most lung, colon, breast, pancreas, prostate, melanoma, lymphoma, or other common cancers.
Yet for approximately 5 to 10 percent of all those with cancer, one mutant gene, passed down in the family DNA, is the primary cause.
The specific DNA mutation typically causes the corresponding protein to lose function. For example, mutations in the genes that lead to inherited forms of breast and ovarian cancer, BRCA1 and BRCA2 (Breast CAncer), prevent the full proteins from being generated; this renders them unable to perform their functions in the cell (it’s like cutting off a boxer’s arms). Because BRCA1 and BRCA2 function to direct the repair of damaged DNA, loss of BRCA1 or 2 activity permits a cell’s DNA to accumulate the damage that can result in cancer.
Inherited genetic mutations are more widely known to cause such medical disorders as hemophilia, sickle cell anemia, Tay-Sachs disease, and muscular dystrophy. But the same principle holds for all inherited genetic diseases: a gene with an important role in the body exists in a mutant form in the affected individuals, leading to a particular health problem. In the case of muscular dystrophy, mutation of a muscle gene called dystrophin causes severe debility. In the case of family cancers, mutations are often in genes that prevent a cell from maintaining its DNA, resulting in mutations to additional genes. These family cancer genes are called cancer susceptibility genes.
