Leaders in Cancer Genetics

Stanford's Cancer Genetics Program doctors and researchers have been instrumental in developing many of the leading technologies used to understand, diagnose, test and screen for hereditary cancer syndromes. This expertise allows our specialists to offer you personalized plans for managing your cancer risk.

Cancer Genetics Program
875 Blake Wilbur Drive
Palo Alto, CA 94304
Phone: 650-498-6000 Getting Here
Maps & Directions
875 Blake Wilbur Drive
Palo Alto, CA 94304
Phone: 650-498-6000 Getting Here

Our Doctors

Care and Treatment of Hereditary Cancers

How Genes Cause Cancer

In order to understand the genetic mechanisms of how genes cause cancer, it is important to review some basic genetic concepts. Genes come in pairs, and work together to make a protein product. One member of the gene pair comes from the mother, while the other member is inherited from the father. Eggs and sperm are called "germ cells." When an alteration or mutation in a gene is present in the germ cells, it is referred to as a "germline mutation." When a germline mutation is inherited, it is present in all body cells. On the other hand, mutations that we are not born with, but that occur by chance over time in cells of the body are said to be "acquired." Acquired mutations are not present in all cells of the body, are not inherited, and are not passed down to our children. Acquired mutations are always involved in causing cancer. Germline mutations are involved in a small percentage of cases.

The formation of tumors basically results from cell growth that gets out of control. In the human genome, there are many different types of genes that control cell growth in a very systematic, precise way. When these genes have an error in their DNA code, they may not work properly, and are said to be "altered" or mutated. An accumulation of many mutations in different genes occurring in a specific group of cells over time is required to cause malignancy. The different types of genes, that when mutated, can lead to the development of cancer are described below. Remember, it takes mutations in several of these genes for a person to develop cancer. What specifically causes mutations to occur in these genes is largely unknown. However, mutations can be caused by carcinogens (environmental factors known to increase the risk of cancer). The development of mutations is also a natural part of the aging process.


Oncogenes are altered forms of genes known as proto-oncogenes. Proto-oncogenes are responsible for promoting cell growth. When altered or mutated, they become oncogenes and then can promote tumor formation or growth.

Properties of oncogenes include the following:

  • Mutations in proto-oncogenes are usually acquired. The exception is that mutations in the RET proto-oncogene can be inherited and cause a condition called multiple endocrine neoplasia type II.
  • Having a mutation in just one of the two copies of a particular proto-oncogene is enough to cause a change in cell growth and the formation of a tumor. For this reason, oncogenes are said to be "dominant" at the cellular level.

Tumor suppressor genes

Tumor suppressor genes are genes normally present in our cells. When working properly, they control the processes of cell growth and cell death (called apoptosis). Through these processes, they can also suppress tumor development. When a tumor suppressor gene is mutated, this can lead to tumor formation or growth.

Properties of tumor suppressor genes include the following:

  • Both copies of a specific tumor suppressor need to be mutated (both members of the gene pair) in order to cause a change in cell growth and tumor formation to occur. For this reason, tumor suppressor genes are said to be "recessive" at the cellular level.
  • Mutations in tumor suppressor genes are usually acquired. The two mutations in a tumor suppressor gene pair may occur as the result of aging and/or environmental exposures.
  • A mutation in a tumor suppressor gene can also be inherited. In these cases, a mutation in one copy of the tumor suppressor gene pair is inherited from a parent, and therefore present in all cells of a person (germline mutation). The mutation in the second copy of the gene (which is necessary for tumor formation and cell growth change) is acquired and usually occurs only in a single cell or a handful of cells. If the second "hit" or mutation occurs in a type of cell that needs this particular tumor suppressor gene to control cell growth, the process of tumor formation will begin. This mechanism is also known as the "two-hit theory."
  • Most of the genes associated with hereditary cancer are tumor suppressor genes. Nonetheless, most mutations in tumor suppressor genes are not inherited.

DNA repair genes

During cell division, the DNA in a cell makes a copy or replica of itself. During this complex process, mistakes may occur. Mismatch-repair genes are DNA repair genes that correct these naturally occurring spelling errors in the DNA. When these genes are altered or mutated, however, mismatches (mistakes) in the DNA remain. If these mistakes occur in tumor suppressor genes or proto-oncogenes, eventually this will lead to uncontrolled cell growth and tumor formation. There are other types of DNA repair genes that repair errors in DNA that occur from mutagenic agents such as large doses of radiation.

Properties of DNA repair genes include the following:

  • Mutations in DNA repair genes can be inherited from a parent or acquired over time as the result of aging and environmental exposures.
  • DNA repair genes require two mutations (both members of the gene pair) in order for the process of tumor formation to occur. For this reason, mismatch-repair genes are said to be "recessive" at the cellular level.

Remember that it takes mutations in several of these genes for cancer to develop. In most cases of cancer, all the mutations are acquired. In inherited cancer, one mutation is passed down from the parent, but the remainder are acquired. Because it takes more than a single mutation to cause cancer, not all people who inherit a mutation in a tumor suppressor gene, proto-oncogene, or DNA repair gene will develop cancer.


Cancer in the Family

Many people have relatives with cancer but when should you be concerned about a genetic cancer risk? Who might benefit from genetic testing and how is it done?

Clinical Trials

Clinical trials are research studies that evaluate a new medical approach, device, drug, or other treatment. As a Stanford Health Care patient, you have access to the latest, advanced clinical trials.

Open trials refer to studies currently accepting participants. Closed trials are not currently enrolling, but may open in the future.

Before beginning treatment, ask your doctor about any clinical trials you should consider. Learn more about clinical trials for cancer patients.

For Patients


Review the New Patient Packet for information about:

  • What to expect on the day of your appointment
  • Maps, directions, parking, public transit options, and contact information
  • Other patient resources

Bring completed forms found in the New Patient Appointment Letter and Pre-Visit Questionnaire.


See the BRCA Decision Tool which guides the management of cancer risks for BRCA1 and BRCA2 mutation carriers.


Please fax the Medical Record Release Form to your new patient coordinator. The medical release form is an authorization form for external facilities to release medical records to Stanford Health Care (formerly Stanford Hospital & Clinics). 

International Patients
Phone: +1 650-723-8561
Email: IMS@stanfordmed.org

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For Health Care Professionals


Phone: 1-866-742-4811
Fax: 650-320-9443
Monday – Friday, 8:30 a.m. – 5 p.m.

Stanford Health Care (formerly Stanford Hospital & Clinics) provides comprehensive services to refer and track patients, as well as provides the latest information and news for physicians and office staff. For help with all referral needs and questions visit Referring Physicians.


Fax a referral form with supporting documentation to 650-320-9443.

Please note, though this form is from Stanford Health Care (formerly Stanford Hospital & Clinics), it is also used for all Cancer Center referrals.

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