Cancer is considered a multifactorial condition. Multifactorial means that both genes and environment play an important role.

Cancer: Environment, inheritance, or both

Most cancers occur due to a combination of both genes and environment. Some forms of cancer, such as lung cancer, are mostly due to environmental factors (i.e., smoking). A few of the known environmental risk factors that can increase a person’s risk for cancer include:

• cigarette smoking
• exposure to asbestos fibers
• eating a high-fat diet

We also know that genes play an important role in cancer, since having a close family member (a mother, father, sister or brother) with cancer increases a person’s risk for developing cancer. Other forms of cancer, such as retinoblastoma (a rare tumor of the back of the eye), are strongly genetic or hereditary.

Cell mutations and inheritance

While all cancers are genetic, not all cancers are inherited. All cancer cells have mutations in their DNA. It is these mutations that cause a once “normal” cell to behave like a cancer cell–one that grows and divides quickly and does not respond to normal checks on cell growth.

Somatic mutations are mutations that only occur within the tumor itself. Somatic mutations cannot be passed down from a parent to a child.

Germline mutations are mutations that are found in all the cells of the body, including the egg cells of a woman or the sperm cells of a man. Germline mutations can be passed down from a parent to a child. Only those mutations that are present in the eggs or sperm can be passed down through a family.

How to know if the cancer in a family inherited

In some families with a very strong history of cancer there may be a germline mutation that is being passed down through the family. These families usually have some features that are “red flags” or clues that there may be a cancer gene in the family. These red flags include:

1. Many family members with cancer in several generations (an “autosomal dominant” pattern of inheritance).
2. An early age at onset of cancer (younger than age 50).
3. A clustering of certain types of cancer, such as breast and ovarian cancer, or colon and uterine cancer.
4. Multiple primary cancers in one person–for example, a woman with both breast cancer and ovarian cancer that occur as separate events. This does not include a cancer that starts in one organ and spreads to another (metastatic cancer).
5. The presence of rare cancers, such as male breast cancer.

Families who have some or all of these features may benefit from meeting with a genetic counselor and/or a geneticist to discuss their family history.

More information about Cancer Genetics:

• Genes, Chromosomes and Cancer Genes
• Cancer Genetic Counseling – Getting the Information You Need
• Inherited Breast Cancer
• Back to the Cancer Genetics Overview

For more information:

Go to the Cancer Genetics health topic.