Is cancer hereditary?

Cancer risks may be inherited or passed from parent to child. Some heritable changes in a person’s genome may lead to an increased risk for developing certain cancers. Even with an inherited risk of cancer, a person is not guaranteed to develop the disease.

Increased cancer risk may be inherited directly due to a specific faulty gene, or may be impacted by a family history of cancer separate from any inherited genetic factors.

Hereditary risk vs. family history

Inherited risk and family history aren’t the same thing, even though some people may use them interchangeably.

• Inherited risks for cancer due to hereditary cancer syndromes are characterized by a known genetic link.
• Having a family history of cancer may increase the risk for developing cancer even in patients who don’t have hereditary cancer syndromes. This may occur due to issues such as a shared environment, lifestyle habits (such as diet) or genetic markers that may raise cancer risk.

According to the American Cancer Society (ACS), about one-third of people in the United States will be diagnosed with cancer at some point, and it’s not uncommon for multiple family members to have cancer. If these cancers develop earlier in life than usual or multiple relatives are diagnosed with the same type of cancer, an underlying genetic cause may be a factor.

Hereditary cancer

With hereditary cancer, parents may pass on genetic changes, also called mutations, that increase the risk of cancer to their children. When this situation occurs in a family, people are said to have a syndrome such as:

• Hereditary cancer syndrome
• Family cancer syndrome
• Inherited cancer syndrome
• Genetic cancer syndrome

Inherited genetic mutations increase a person’s risk of certain cancers and make it more likely that cancer occurs at an earlier age. There may also be additional, non-cancer growths or associated conditions, such as benign (non-cancerous) tumors as a part of a hereditary cancer syndrome.

When someone inherits a mutation, less acquired DNA damage is needed for cells to become cancerous, making the path to cancer more likely. While cancer risks are higher, having an inherited mutation does not guarantee that cancer will develop.

Hereditary cancer syndromes are more likely if multiple relatives have the same or related cancers, especially across generations and in close relatives on the same side of the family. People with inherited risks for cancer are more likely to develop cancer at younger ages or have more than one cancer diagnosed. If there are rare cancers in a family (such as breast cancer in men), family members may inherit those risks.

Family history of cancer

A family history of cancer may impact risks even when an inherited mutation is not present. Cancer may be considered familial when two or more relatives are diagnosed with cancer, especially the same type of cancer.

Most of the time, the reason for cancer clustering in a family is unknown. There may be minor DNA changes that aren’t part of hereditary cancer syndromes that may combine to increase cancer risk. Shared environmental or lifestyle factors (such as exercise, diet or tobacco use) in families may also impact cancer risk.

Cancers in immediate family members, such as a sibling or parent, are more impactful on risk than when more distant relatives are diagnosed because of the amount of shared DNA among relatives. When looking at relatives outside of the immediate family, it’s most helpful to examine each branch independently. Two cases of breast cancer on the mother’s side is more significant than one on each side of an extended family.

What percentage of cancer is hereditary?

Hereditary or genetically linked cancers are less common than those caused by environmental or lifestyle factors and those with no specific cause. Of all cancers, about 5 percent to 10 percent are linked to hereditary cancer syndrome, according to ACS.

For many cancer types, the risk factors are not inherited. For example, most cases of cervical cancer are due to the human papillomavirus (HPV). Smoking or other environmental pollutants, like radon, cause most lung cancer cases.

Which types of cancer are more likely to be hereditary?

Ovarian, fallopian-tube-cancer and primary peritoneal cancers are among the most likely cancers to be linked with inherited risk factors. Inherited mutations are detected for about 20 percent of people with these diagnoses. About 5 percent to 10 percent of most other cancers are caused by inherited mutations.

Breast, ovarian and other cancers of the female and male reproductive systems: Hereditary breast and ovarian cancer syndrome (HBOC), usually caused by inherited BRCA1 and BRCA2 mutations, increases the risks for breast, ovarian, fallopian tube, primary peritoneal, prostate, and pancreatic cancer, as well as melanoma. Many of these genetic changes are in the BRCA1 and BRCA2 genes, while some are unknown or based on family history. Less commonly, pancreatic cancer and peritoneal cancer cases are linked to this syndrome. Other family cancer syndromes, like Peutz-Jeghers syndrome, are associated with some of these cancer types.

Breast, uterus and thyroid cancers: People with Cowden syndrome are at increased risk for these and other cancers, and often have benign growths on the skin, in the mouth and in the intestinal tract.

Leukemia (cancer of the white blood cells): Inherited genetic disorders and certain bone marrow diseases may increase the risk of acute myeloid leukemia and other types of leukemia.

Colon and rectal (colorectal) cancer: Lynch syndrome, also called hereditary non-polyposis colorectal cancer (HNPCC), causes increased risks for developing colorectal and other cancers, including:

• Endometrial and uterine cancer 
• Ovarian cancer
• Stomach cancer
• Small intestine cancer 
• Pancreatic cancer
• Kidney cancer 
• Brain cancer
• Skin cancer
• Breast cancer
• Prostate cancer
• Cancer of the ureters
• Bile duct cancer

Colon cancers are also linked to familial adenomatous polyposis (FAP), a less common cancer syndrome in which patients may have a large number of colon polyps or growths called adenomas.

Sarcoma, breast, brain, leukemia and adrenal gland cancers: These cancers are linked to Li-Fraumeni syndrome. Sarcomas may include osteosarcoma of the bone and soft tissue sarcomas, and cancers of the muscles, connective and other bodily tissues.

Other cancer syndromes that may increase the risk of soft tissue sarcomas include:

• Neurofibromatosis
• Tuberous sclerosis
• Gorlin syndrome

Thyroid, pituitary, parathyroid and pancreatic cancers: These cancers are linked to multiple endocrine neoplasia (MEN) type 1 and 2 syndromes. People with MEN2 are at increased risk of a rare cancer type called medullary thyroid cancer.

Stomach and breast cancers: Patients with hereditary diffuse gastric cancer syndrome (HDFC) are at higher risk of developing a rare type of stomach cancer. This inherited cancer syndrome also increases the risk of breast cancer.

Melanoma (skin cancer) and pancreatic cancer: These cancers are linked to mutations in the CDKN2A gene.

Eye cancer (retinoblastoma): The increased risk of this cancer is linked to a family cancer syndrome called hereditary retinoblastoma.

Kidney cancer: Family cancer syndromes such as von Hippel-Lindau disease, Birt-Hogg-Dube’ syndrome and others increase the risk of kidney cancer.

Genetic testing and genetic counseling

Genetic testing is done using blood, saliva and sometimes skin samples to search certain genes for inherited mutations.

While people with strong personal and family histories of cancer are more likely to have inherited risks, research has shown that people with less striking histories may also have hereditary cancer syndromes. Some family history clues that increase the chances of an inherited risk for cancer may include:

• Cancers diagnosed at earlier ages, especially at age 50 or younger
• Multiple relatives with the same or related cancers (for example breast/ovarian or colon/endometrial cancer)
• More than one cancer in the same person
• Cancer in multiple generations
• Rare cancers/tumors

Genetic counselors are medical professionals who evaluate personal and family histories for the possibility of inherited risks for developing cancer, educate people about genetics topics and testing, counsel people to help them make informed decisions and adapt to risks or a genetic condition, and interpret and convey genetic test results to patients and clinicians.

The psychological and emotional support of genetic counseling may be especially helpful for cancer previvors, people who haven’t had cancer but are at a higher risk of developing it. They require closer cancer screening and may be offered surgeries or interventions to reduce cancer risks.