Types of cancer

For many types of cancer, a portion of those cancers are linked to a family history. Breast, ovarian, prostate, and colon are some of these cancers. Some of these are discussed briefly here, but only to help explain heredity and cancer. Please refer to the American Cancer Society specific cancer site documents for more information about a particular type of cancer and its genetic components, diagnosis, and treatment.

Breast cancer

Many women are concerned that breast cancer seems to run in their family. A woman who has a first-degree relative (a mother, sister, or daughter) with breast cancer is about twice as likely to develop breast cancer as a woman without a family history of this cancer. Still, most cases of breast cancer, even those in close relatives, are not part of a family cancer syndrome caused by an inherited gene mutation.

The chance that someone has an inherited form of breast cancer is higher the younger they are when they get the cancer and the more relatives they have with the disease. Inherited breast cancer can be caused by several different genes, but the most common are BRCA1 and BRCA2. Inherited mutations in these genes cause hereditary breast and ovarian cancer syndrome (HBOC). Along with breast and ovarian cancer, this syndrome can also lead to male breast cancer, pancreatic cancer, prostate cancer, as well as some others. This syndrome is more common in women of Ashkenazi Jewish descent than it is in the general US population.

Women with a strong family history of breast cancer may choose to undergo genetic counseling to estimate their risk for inherited breast cancer. They then can choose to be tested to find out if they have a breast cancer gene mutation. If a mutation is present, the woman has a high risk of developing breast cancer. She may start getting mammograms at an age younger than 40, have special breast cancer screening tests, or take other measures to try to reduce her risk of getting breast cancer.

Colon cancer

One cause of hereditary colon cancer is a disease called familial adenomatous polyposis (FAP). People with this disease start getting colon polyps by their teen years, and over time may have hundreds of polyps in their colon. If left alone, at least one of these polyps will become cancer. The gene for this syndrome is called APC, and testing for mutations in this gene is available. If FAP is diagnosed early in life, surgery to remove the colon is often used to stop the cancer from developing.

The most common inherited syndrome that increases a person's risk for colon cancer is called hereditary non-polyposis colorectal cancer (HNPCC), or Lynch syndrome. People with this syndrome have a high risk of colorectal cancer. Most of these cancers occur before age 50. People with HNPCC may also have polyps, but they only have a few, not hundreds as in FAP. HNPCC also leads to a high risk of endometrial cancer (cancer in the lining of the uterus) in women. Other cancers linked with HNPCC include cancer of the ovary, stomach, small intestine, pancreas, kidney, brain, ureters (tubes that carry urine from the kidneys to the bladder), and bile duct.

HNPCC is caused by mutations in one of the DNA repair enzyme genes MLH1, MSH2, MSH6, PMS1, or PMS2. Mutations in these genes can be found through genetic testing. Another option for people with colorectal cancer is to have the tumor tissue tested for changes that can be caused when one of these genes is faulty. These changes are known as microsatellite instability (or MSI). Having normal findings (no MSI) implies that HNPCC is not present and that the genes that cause it are normal.

Someone who is known to carry an HNPCC gene mutation may start colonoscopy screening at an early age (such as during their early 20s) to find cancers and polyps early. Some people even have surgery to remove of most of the colon to try to prevent cancer from starting. Women with HNPCC may choose to be screened for endometrial cancer. Some even have their uterus removed after they have finished having children.

Childhood cancers

Like adult cancers, most childhood cancers are not inherited. They are caused by mutations acquired during the child's life. Some of these may even have occurred before the child was born (while still in the womb). A few types of childhood cancers are known to occur more often in some families. Some of these are due to hereditary cancer syndromes.

Retinoblastoma: This is a childhood cancer that starts in the eye. It can be caused by an inherited mutation in the tumor suppressor gene Rb. In about 1 out of 4 children with retinoblastoma, the abnormal gene is in every cell in the body. In most of these cases, this is due to a new mutation (gene change) in the sperm or egg. In some cases though, the abnormal copy of Rb was inherited from a parent.

Even though the child has a remaining normal copy of the Rb gene, he or she is likely to develop this cancer. This is because there is no backup to stop the mutated gene from making abnormal cells if the remaining healthy Rb gene stops working in even one cell.

Patients with the hereditary form of retinoblastoma are more likely to get tumors in both eyes. They also have an increased risk of developing other types of cancer, including cancers of the bone, brain, nasal cavities, and a type of skin cancer (melanoma).

Li-Fraumeni syndrome: This syndrome occurs when a person inherits a mutation in the gene for p53 (TP53, a tumor suppressor gene). A normal gene for p53 stops the growth of abnormal cells. People with a TP53 gene abnormality have a higher risk of childhood sarcoma, leukemia, and brain (central nervous system) cancers.

Li-Fraumeni syndrome also raises the risk of cancers of the breast and adrenal glands. One study showed that 15% of Li-Fraumeni patients who had cancer were diagnosed later with a second cancer, and some developed a third and fourth cancer later on.