Genetic
Screening of Cancer
Researchers have identified 20 to 30 cancer-susceptibility
genes that greatly increase a person's odds of getting
some form of malignancy. For example, a gene has been
identified on chromosome number 9 that may be linked
to a common skin cancer called basal cell carcinoma.
This gene labeled PTC or patched, may someday be important
in screening for this type of cancer. Another gene,
called HNPCC, is carried by one out of every 300 Americans
and may greatly increase an individual's chance of getting
colon cancer. And the doubly dangerous gene called BRCA-1
seems to give women an 85% chance of developing breast
cancer, as well as a 50% chance of ovarian tumors.
BRAC1 and BRCA2
Approximately 10 to 15 percent of all breast cancers
are thought to be familial and about one third of these
cases are due to an inherited mutation in a BRCA1 or
BRCA2 breast cancer susceptibility gene. BRCA1 and 2
mutations are associated with early-onset breast cancer,
and some experts call for aggressive Screening of affected
persons.
BRCA1 is a gene on chromosome 17 that is known to be
involved in tumor suppression. A woman with certain
known mutations in BRCA1 has a lifetime risk of 56 to
85 percent for breast cancer and an increased risk of
ovarian cancer. Of women with breast cancer, a BRCA1
mutation has been found in 0.3 percent (one of 333)
and of women in the general population, in 0.12 percent
(one of 833). In Ashkenazi Jewish women (most Jewish
people in the United States are of this Eastern European
origin), BRCA1 mutations occur in 1 percent.
BRCA2 is another susceptibility gene for breast cancer
and is found on chromosome 13. Mutations in BRCA2 confer
an elevated breast cancer risk similar to that occurring
with BRCA1 mutations. As with BRCA1, BRCA2 is also found
in 1 percent of Ashkenazi Jewish women. A woman’s
lifetime chance of developing breast and/or ovarian
cancer is greatly increased if she inherits an altered
BRCA1 or BRCA2 gene.
Women with an inherited alteration in one of these genes
may also have an increased chance of developing colon
cancer. Men with an altered BRCA1 or BRCA2 gene also
have an increased risk of breast cancer (primarily if
the alteration is in BRCA2), and possibly prostate cancer.
Alterations in the BRCA2 gene have also been associated
with an increased risk of lymphoma, melanoma, and cancers
of the pancreas, gallbladder, bile duct, and stomach
in some men and women.
Benefits of Screening
In a family with a history of breast and/or ovarian
cancer, it may be most informative to first test a family
member who has the disease. If that person is found
to have an altered BRCA1 or BRCA2 gene, the specific
change is referred to as a "known mutation." Other family
members can then be tested to see if they also carry
that specific alteration. In this scenario, a positive
test result indicates that a person has inherited a
known mutation in BRCA1 or BRCA2 and has an increased
risk of developing certain cancers, as described above.
However, a positive result provides information only
about a person's risk of developing cancer. It cannot
tell whether cancer will actually develop-or when. It
is also impossible to predict the effectiveness of special
screening or preventive medical procedures for people
with alterations in BRCA1 or BRCA2. Not all women who
inherit an altered gene will develop breast or ovarian
cancer.
A positive test result may have important health and
social implications for family members, including future
generations. Unlike most other medical tests, genetic
tests can reveal information not only about the person
being tested, but also about that person's relatives.
Both men and women who inherit an altered BRCA1 or BRCA2
gene, whether or not they get cancer themselves, may
pass the alteration on to their sons and daughters.
However, not all children of people who have an altered
gene will inherit the alteration.
A negative test result will be interpreted differently,
depending upon whether there is a known mutation in
the family. If someone in a family has a known mutation
in BRCA1 or BRCA2, testing other family members for
that specific gene alteration can provide information
about their cancer risk. In this case, if a family member
tests negative for the known mutation in that family,
it is highly unlikely that they have an inherited susceptibility
to cancer. This test result is called a "true negative."
Having a true negative test result does not mean that
a person will not get cancer; it means that the person's
risk of cancer is the same as that of the general population.
In cases where no known mutation in BRCA1 or BRCA2 has
previously been identified in a family with a history
of breast and/or ovarian cancer, a negative test is
not informative. It is not possible to tell whether
a person has an alteration in BRCA1 or BRCA2 that was
not identified by the test (a false negative), or whether
the result is a true negative. In addition, it is possible
for people to have an alteration in a gene other than
BRCA1 or BRCA2 that increases their cancer risk, but
is not detectable by this test.
Sample required for the analysis
7 ml EDTA blood in special monovettes or vacutainers,
not normal EDTA tubes. When drawing specimen, please
wear gloves and use the tubes which is provided by us.
DO NOT centrifuge and DO
NOT take aliquots for other analysis.
How long and How much
Reports with comments will be delivered within 4-6 weeks
times. Check the Price List
to get the price.
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