The Cancer Genetics Clinic is part of Stanford's
Cancer Center, a National Cancer Institute-designated center
offering genetic counseling and testing for individuals concerned with
the risk of an inherited cancer predisposition. The clinic staff
includes medical oncologists, genetic counselors, and geneticists.
When a healthcare provider looks at a family's medical history to
determine whether the cancer in a family is hereditary, he/she starts
by asking the following questions:
How many persons in the family have cancer?
type(s) of cancer are present in the family?
someone who has more than one type of cancer?
What are the
ages of onset of cancer?
What is the gender of the
individuals with cancer?
Are the cancers unilateral
(occurring on one side of the body) or bilateral (i.e., both
What type of environmental exposures or lifestyle
factors do the persons with cancer have that might have influenced
their risk of cancer (i.e., are they smokers)?
How are the
persons with cancer related to one another?
Is there a
vertical pattern of inheritance observed (parents with cancer who
have children with cancer)?
What is the ancestry and
ethnicity of the family?
All of this information is recorded in the form of a family tree,
called a pedigree. The information is used to try to classify the
family history into one of three categories described below. Often,
additional information such as medical records or results of genetic
testing may be gathered to aid in the classification process.
Classifying the family history helps in determining whether relatives
have an increased chance of developing specific types of cancer, how
great the risk of cancer might be, and whether genetic testing might
be helpful in further evaluating cancer risks in the family.
What is sporadic cancer?
The word sporadic means "to occur by chance." Families who
have a single person with cancer at an older age are usually
classified as "sporadic." In other words, there is not an
inherited pattern of cancer present, and often only one or two
individuals in the family have cancer at a typical age of onset.
Relatives are usually not at increased risk of developing cancer.
Genetic testing is usually not beneficial in these families.
What is familial cancer?
When there are more cases of cancer in a family than chance alone
would predict, but the features of hereditary cancer (described below)
are not present, a family is said to have "familial cancer."
In other words, in these cases, there is a cluster of cancers in the
family, but no clear pattern of inheritance, and the cancers occur at
the average age of onset. Familial cancers may be due to a combination
of genes and shared lifestyle factors or environmental exposures
On the other hand, some of these histories can represent a chance
occurrence of sporadic cancers. A familial history may also arise due
to a single gene mutation (hereditary cancer) that has reduced
penetrance (a mutation associated with lower cancer risks and later
onset of cancer). In general, with familial cancer, close relatives
have a modestly increased risk of developing the cancer in question.
The chance that genetic testing will be beneficial in further
assessing cancer risks is usually small.
What is inherited cancer?
These families have multiple family members with the same or related
cancers. The cancers tend to occur at younger than average ages
(usually <50 years). Also, there is often a history of persons who
developed two or more separate cancers; i.e., colon cancer in a breast
cancer survivor, bilateral cancers (bilateral breast cancer), or
multifocal cancers (two or more cancers in the same organ such as two
separate colon cancers).
Families with inherited cancer often have cancer in two or more
generations with cancer displaying an autosomal dominant pattern of
inheritance. In other words, when a parent has inherited
predisposition to cancer, each child has a 50/50 (one in two) chance
of inheriting the predisposition. Those in the family that inherit the
predisposition have a high chance of developing the associated
cancers. Those who do not inherit the predisposition are not at
increased cancer risk.
Genetic testing can often be beneficial in determining who in the
family has an increased cancer risk. In most cases, it is important to
test a relative with cancer first, to see if a causative mutation can
be identified, before testing relatives who have not had cancer.
James Ford, MD, director of the Stanford Cancer Genetics Program, has always been fascinated with figuring out how genetics influences cancer. His interest is in working with families to lower their risk of familial cancer.
This video explains how genetic counselors at Stanford’s Cancer Genetics Clinic help families understand if they have a hereditary cancer syndrome and an elevated risk for colon cancer.
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See the BRCA
Decision Tool which guides the management of cancer risks for
BRCA1 and BRCA2 mutation carriers.
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