Genetics Northern California

Cancer Genetics

Cancer is caused by harmful genetic changes in cells of the body. It starts when a cell builds up enough harmful changes in the DNA to interfere with normal growth. The cell grows out of control and can spread to other parts of the body. This is a long process that takes many years and involves many genetic changes. For most cancers, all of the genetic changes happen after a person is born. They are due to aging and exposure to things in the environment. 

But some cancers are related to cancer risk genes that can be passed from parent to child. When a person inherits a cancer risk gene that is not working, all the cells in the body start with that harmful genetic change. This makes a person more likely to develop cancer. Cancer risk genes can cause many different types of cancer, including breast and ovarian cancer, colon cancer, uterine cancer, kidney cancer, and medullary thyroid cancer. About 5% to 10% of common cancers are related to a harmful change in a cancer risk gene.  

Families with inherited cancer risk are more likely to have:

  • Many people in the family with similar or related cancers

  • Cancer in two generations of the family (or more)

  • Cancer that develops early (often in the 30s or 40s)

  • People who have had more than one cancer (Example: colon cancer and uterine cancer; or cancer in both breasts)

How common is it to have several family members with cancer?
It is very common to have family members with cancer. This is because about 1 in 3 Americans develop some type of cancer during their lifetime. That means many people have more than one family member with cancer. 

Some cancers, such as breast cancer and prostate cancer, are so common that there could be two affected relatives just by chance. Cancer in people from the same family could be due to a common lifestyle or shared environment. There are also families that have small genetic differences that make them more sensitive to cancer-causing exposures. However, some families have an inherited cancer risk with a higher risk of cancer. 

What should I do if I am worried about inherited cancer risk?  

  1. Talk to your doctor or nurse practitioner. Your health care provider can help you decide if talking with a Genetics specialist would be useful. You can also contact the Kaiser Permanente Genetics Department and ask for an appointment.    
  2. Gather your family history.  You can use our family history form to help track the cancer history in your family.   
  3. Request medical records. When possible, ask family members with cancer for their medical records. Pathology reports and genetic test results are very useful. These records can be important in estimating your inherited cancer risk.
To learn more about genetic testing in a family: Hereditary Cancer Risk: Who should be tested first?

Last reviewed: January 22, 2021
Reviewed by: Kimberly Barr, MS LCGC