Hereditary cancer syndrome is a term used when several members of a family have cancer because of an inherited abnormal (mutated) gene. Increased risk of cancer is associated with hundreds of hereditary conditions, according to the National Cancer Institute (NCI).

Some of the more prominent of these include:

• Breast cancer. About 5 to 10 percent of breast cancers are associated with known mutated genes, especially the BRCA1 and BRCA2 genes. These mutations can raise the lifetime risk of breast cancer by 80 percent, according to the American Cancer Society (ACS). Some of these mutations have also been found to increase the odds of getting ovarian cancer. In addition, men with BRCA1 mutations have an increased risk of developing prostate cancer. Other genes have also been identified that may increase the risk of breast cancer.

• Familial prostate cancer. Male carriers of the two main gene mutations involved in hereditary breast cancer have three to four times the risk of prostate cancer. Other gene mutations have also been implicated in prostate cancer.
  
  
• Hereditary causes of colorectal cancer, including hereditary nonpolyposis colon cancer (HNPCC) and familial adenomatous polyposis (FAP). These conditions, featuring polyps that may become malignant, are estimated to account for up to 15 percent of cases of colorectal cancer. Sometimes people with such conditions have the colon surgically removed as a preemptive measure.
  
  
• Familial melanoma. Several melanoma-predisposing autosomal dominant genes have been identified. An estimated 5 to 7 percent of people with melanoma come from genetically high-risk families.
  
  
• Neurofibromatosis. Type 1 affects one person in 4,000 and involves skin discoloration and tumors that become malignant in up to 5 percent of case. People with type 1 have a higher risk of developing other cancers, such as brain tumors and leukemia. Type 2 affects one person in 50,000 and often affects the acoustic (hearing) nerve. Surgery may be needed with type 2 to avoid loss of hearing.
  
  
• Fanconi’s anemia. An autosomal recessive condition associated with about 20 percent of case of childhood aplastic anemia. It is more common in Ashkenazi Jews. Multiple birth defects are common. Signs include bleeding, anemia and easy bruising. Average age of diagnosis is 6 years. 

Family cancer syndromes also have been found in other forms of cancer, including:

• Brain tumors
• Hodgkin’s lymphoma
• Kidney cancer
• Melanoma
• Pancreatic cancer
• Retinoblastoma
• Testicular cancer
• Thyroid cancer

Scientists are working on identifying, treating and preventing hereditary cancers. Progress has accelerated since the Human Genome Project was completed in 2003. This international effort included identification of all human genes. Scientists at the National Institutes of Health are attempting to create a Cancer Genome Atlas to identify all the genes in cancer. The project will begin by studying three cancers: glioblastoma, lung cancer and ovarian cancer. A separate study recently completed at Johns Hopkins University identified 189 genes mutations in breast cancer and colon cancer.

Researchers are using the data to improve genetic tests and gene therapy.