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Untitled Document
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| Breast
and Ovarian Cancer |
| The Testing Process When the Mutation in Your
Family is Already Known |
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By
Kathleen Fergus,
MS, CGC and Jill
Simonsen
Reviewed
by Beth Crawford,
MS, CGC and Miriam
Komaromy, MD
Last
updated September 11, 2000
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For
people who come from families in which a mutation
has already been identified, genetic testing
is a much simpler and less ambiguous laboratory process
than it is for families in which a mutation has not
yet been detected. Since the truly hard work of pinpointing
the genetic culprit for a family's breast and ovarian
cancers has already been performed, subsequent testing
can examine just that specific site on either the BRCA1
or BRCA2 gene
where a specific mutation
is known to occur. This type of DNA test — which
looks for one mutation in a specific region of a single
gene — is called site-specific analysis, and it's
only useful in members of families in which a mutation
has already been identified.
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The Test
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In
the genetic test known as single-site analysis, scientists
examine just one location on an individual's DNA
for a specific mutation that's already been identified
in other family members. In the case of breast and ovarian
cancer, this means that a lab is looking at just a tiny
portion of either the BRCA1 or BRCA2 gene for one particular
change rather than examining both of these very large
genes for any of the hundreds of mutations known to
be associated with these types of cancer, as is the
case with DNA sequencing. Not surprisingly, single-site
analysis is much less expensive and time-consuming than
DNA sequencing.
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Interpreting
the Results
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Because
this form of genetic testing is used to detect a specific
known mutation in the BRCA1 or BRCA2 gene, there's no
chance of getting an ambiguous result. The mutation
known to be the cause of a family's cancer is either
present or it is not.
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Positive result. If single-site analysis reveals
a mutation, this is referred to as a positive result.
The person being tested has inherited the family's
predisposition to breast and ovarian cancer and should
talk to a doctor about what she can do to reduce her
risk, including following more aggressive screening
guidelines, making certain lifestyle changes, and
considering the use of preventive medications and/or
surgery.
- Negative
result. If
single-site analysis doesn't detect a mutation, this
is referred to as a negative result. The person being
tested has not inherited the family's predisposition
to breast and ovarian cancer. It's important to understand,
however, that a negative test result does not mean
that an individual is risk-free; no one is that lucky.
It simply means that the person is at the same risk
for these diseases as the general population and should
follow regular screening guidelines for breast and
ovarian cancers.
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Single-Site
Testing: One Family's Story
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Jennifer
is a 32-year-old woman who has never had cancer.
She is in a serious relationship but does not yet
have children. She receives a letter from her maternal
aunt, Dorothy, a 48-year-old woman who was recently
diagnosed with breast cancer. Dorothy's mother (Jennifer's
maternal grandmother) was also diagnosed with breast
cancer at age 47 — a fact that convinced Dorothy
(after her diagnosis and initial round of therapy)
to undergo testing for one of the mutations known
to predispose to breast and ovarian cancer.
DNA
sequencing of both the BRCA1 and BRCA2 genes revealed
that Dorothy did indeed have a mutation in the
BRCA2 gene. Although Jennifer's mother can't undergo
testing for the same mutation since she died in
a car accident when Jennifer was a child, Jennifer
understands that her mother had a 50 percent chance
of carrying the same mutation as her sister did.
This means that Jennifer has a 25 percent chance
of having the same mutation as her aunt.
Although
Jennifer is not sure she's at the right point
in her life to undergo genetic testing, she decides
to talk to a genetic counselor to learn about
her options as well as the steps she can take
to reduce her risk for disease.
The
Decision
After
talking to the counselor, Jennifer learns that
if she were to go ahead with genetic testing,
the most appropriate method for her would be single-site
analysis. Because DNA sequencing has already revealed
the mutation causing her family's cancers, Jennifer's
test only needs to look for the specific mutation
in just one gene (rather than the range of mutations
across both the BRCA1 and BRCA2 genes that DNA
sequencing can detect).
Jennifer
understands that if single-site analysis reveals
a mutation, she has inherited the increased risk
for breast and ovarian cancer that runs in her
family and can talk to her doctor about taking
steps to reduce her risk for these diseases. If,
on the other hand, single-site analysis does not
detect a mutation, Jennifer will know that she
has not inherited an increased risk for breast
or ovarian cancer because her cancer risk is no
greater than that of someone who does not have
a family history of cancer, and she can follow
the screening guidelines recommended for the general
population.
After
considering all of her options, Jennifer decides
to delay genetic testing. Because she's currently
between jobs, she's worried that a positive test
result might jeopardize her health and life insurance.
She plans to undergo single-site analysis after
her job situation has stabilized. In the meantime,
she has decided to take oral contraceptives to
decrease her risk for ovarian cancer and has worked
out a screening plan for breast and ovarian cancer
with her physician.
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References
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Arnold, N. et al. (1999). A highly sensitive, fast,
and economical technique for mutation analysis in hereditary
breast and ovarian cancers. Hum Mutat 14(4):
333-9.
Biesecker, B. B. and Brody, L.C. (1997). Genetic susceptibility
testing for breast and ovarian cancer: a progress report.
J Am Med Womens Assoc 52(1): 22-7.
Frank, T. S. and Braverman, A.M. (1999). The pros and
cons of genetic testing for breast and ovarian cancer
risk. Int J Fertil Womens Med 44(3): 139-45.
Mann, G. B. and Borgen, P.I. (1998). Breast cancer genes
and the surgeon. J Surg Oncol 67(4): 267-74.
Neuhausen, S. L. and Ostrander, E.A. (1997). Mutation
testing of early-onset breast cancer genes BRCA1 and
BRCA2. Genet Test 1(2): 75-83.
Shattuck-Eidens, D., A. et al. (1997). BRCA1 sequence
analysis in women at high risk for susceptibility mutations.
Risk factor analysis and implications for genetic testing
[see comments]. JAMA 278(15): 1242-50.
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