USC CLINICAL
GENETICS
UNDERSTANDING YOUR
FAMILY HISTORY OF COLON CANCER
UNIVERSITY OF
SOUTH CAROLINA
SCHOOL OF MEDICINE
DEPARTMENT OF OBSTETRICS
AND GYNECOLOGY
DIVISION OF GENETICS
Location:
Two Medical Park
Suite 301
Columbia, SC 29203
Phone:
803-779-4928 ext. 228
Toll free in SC:
800-544-9866
Fax: 803-434-6852
(laboratory)
Fax: 803-434-4596
(genetic counselors)
E-mail:
uscgenetics@medpark.sc.edu
Web:
www.med.sc.edu/uscgenetics
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Colorectal cancer is the third most common cancer
diagnosed in the United States. In 2000 alone, an
estimated 135,000 new cases were diagnosed. The chance
that a person will develop colorectal cancer in his or her
lifetime approaches 6%.
Family History:
Most cases of colorectal cancer occur by chance in individ-
uals who do not have any family members diagnosed with
cancer. However, 5-10% of people who develop colorectal
cancer will have a significant family history of the condi-
tion.
For some people, having a family history of colorectal can-
cer means that they have a high chance of developing the
disease, and in some cases, other cancers as well. Cancer
runs in these families due to an inherited mutation in a sin-
gle, cancer-predisposing gene. This is called hereditary
cancer.
How Do People Determine
if They Have Hereditary Cancer?
Determining the significance of a family history requires a
process called "Cancer Risk Assessment". This process
begins by constructing a family tree to see who in the fam-
ily has been diagnosed with cancer and what types of can-
cers they have had. Additional factors important in analyz-
ing the family history include the ages at which cancer
diagnoses were made and whether a person has had more
than one kind of cancer. The family history information is
collected on immediate relatives (brothers, sisters, children,
parents) as well as more distant relatives (grandparents,
aunts, uncles, and cousins).
If the family history shows a pattern of hereditary cancer,
then genetic testing may be an option. Such testing allows
scientists to lo