Heredity

Main article: Cancer syndrome

The vast majority of cancers are non-hereditary, which are called sporadic cancers. Hereditary cancers are cancers that are primarily caused by an inherited genetic defect. Less than 0.3% of the population are carriers of a genetic mutation which has a large effect on cancer risk.^[26] They cause less than 3–10% of all cancer.^[26] Some of these syndromes include:

• certain inherited mutations in the genes BRCA1 and BRCA2 with a more than 75% risk of breast cancer and ovarian cancer^[26]
• 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 ofcolon 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.