Heredity

Most forms of cancer are sporadic, meaning that there is no inherited cause of the cancer. There are, however, a number of recognised syndromes where there is an inherited predisposition to cancer, often due to a defect in a gene that protects against tumor formation. Famous examples are:

• certain inherited mutations in the genes BRCA1 and BRCA2 are associated with an elevated risk of breast cancer and ovarian cancer
• tumors of various endocrine organs in multiple endocrine neoplasia (MEN types 1, 2a, 2b)
• Li-Fraumeni syndrome (various tumors such as osteosarcoma, breast cancer, soft tissue sarcoma, brain tumors) due to mutations of p53
• Turcot syndrome (brain tumors and colonic polyposis)
• Familial adenomatous polyposis an inherited mutation of the APC gene that leads to early onset of colon carcinoma.
• Hereditary nonpolyposis colorectal cancer (HNPCC, also known as Lynch syndrome) can include familial cases of colon cancer, uterine cancer, gastric cancer, and ovarian cancer, without a preponderance of colon polyps.
• Retinoblastoma, when occurring in young children, is due to a hereditary mutation in the retinoblastoma gene.
• Down syndrome patients, who have an extra chromosome 21, are known to develop malignancies such as leukemia and testicular cancer, though the reasons for this difference are not well understood.