All cancers are caused by changes to materials in our bodies called “genes.” These are units of information in every cell of our bodies. Genes tell our bodies which proteins to make based on the type of cell and its needs. Some genes tell our bodies how to fix damage accumulated over time from normal aging, environmental toxins, sun exposure, dietary factors, hormones, and other influences. These damage-controlling genes can repair cells or tell cells when to stop growing and die if there is too much damage to repair. When genes themselves are damaged, they can develop changes called “mutations.”

For most people who develop cancer, the cancer-causing gene mutations happen over the course of a lifetime, leading to cancer later in life. Some people are born with a gene mutation that they inherited from their mother or father. This damaged gene puts them at higher risk for cancer than most people. When cancer occurs because of an inherited gene mutation, it is referred to as “hereditary cancer.” The pattern of familial clustering is more in some cancer like breast cancer, colon cancer, and ovarian caner but less in many other types of cancers like lung cancer, prostate cancer, and esophageal cancer.

Sometimes the increased risk for breast cancer may be due to a genetic mutation. BRCA1 and BRCA2 are examples of genetic mutation that gives rise to increased risk of breast cancer. Women who have this mutation have about 60% lifetime risk of developing breast cancer. Women with these mutations also have significantly higher risk of developing ovarian cancer. This mutation is genetically transmitted to off springs in an autosomal dominant model. This means that son or daughter of BRCA mutation carrier has 50% risk of acquiring the mutation. It is to be noted that only about 5% breast cancers belong to this category where a specific genetic mutation can be identified. Apart from identifiable genetic mutation that increases the risk of breast cancer, presence of a family member with breast cancer would increase the risk of development of breast cancer in a woman.  Family Health Questionnaire .

A similar situation is present in colon cancer as well, there are specific identifiable genetic mutations that gives rise to very high risks of developing colon cancer. Mutation in the APC gene is a noted example. If a person carries this mutation that person has close to 100% risk of developing colon cancer in the late adulthood. This gene is transmitted in an autosomal dominant model, which means that any offspring of the carrier has a 50% risk of inheriting this mutation and subsequent increased risk of colon cancer. As with breast cancer most cases of colon cancer are not related genes that could be tested. Colon cancer diagnosis in a person would increase the risk of colon cancer development in his close relatives. Again as mentioned above this is not the result of a single genetic abnormality that is inherited, but is really due to interaction of a group of genes and various environmental factors common to the family like eating habits and food preferences.

The following is a list of identified familial genetic syndromes associated with a single genetic abnormality. This is not a comprehensive list of all known disorders.

Autosomal dominant disorders