Heredity

Most forms of cancer are "sporadic", and have no basis in heredity. There are, however, a number of recognised syndromes of cancer with a hereditary component, often a defective tumor suppressor allele. 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.