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Why isn't the CA-125 a
good
general screening test?
The CA125 test stands for Cancer Antigen
and measures a human protein that is in a number of human
tissues.
All women want a test to
detect ovarian and other cancers of the reproductive system. The PAP
test effectively tests for cervical cancer. As a result, early
detection of cervical cancer has improves. However, ovarian &
other reproductive cancers are rarely detected by the PAP test.
Sadly, there is no blood
test that is sensitive and specific for ovarian cancer.
CA125 is not specific. A
highly specific test identifies a clear type of condition. However,
positive test results can be obtained from menstruation, endometriosis,
pregnancy and other conditions.
In addition the CA125 in
not very sensitive. Sensitivity is important because a reliable test
should accurately detect a condition. The CA125 does not.
Johns Hopkins reports,
"The
CA125 test only returns a true positive result for about 50% of Stage I
ovarian cancer patients. The CA125 test is not an adequate early detection
tool when used alone.
The
CA125 test has an 80% chance of returning true positive results from stage
II, III, and IV ovarian cancer patients. The other 20% of ovarian cancer
patients do not show any increase in CA125 concentrations."
Thus, we found a great
clinical consensus well stated by Dr.
Diane Bodurka, assistant professor in M. D. Anderson's Department of
Gynecologic Oncology, in CancerWise's Sept 2001 e-newsletter:
"The
problem with CA125 is two-fold," Dr. Bodurka said. "In half of
the ovarian cancer cases that are diagnosed early - that is, when the
cancer is limited to the ovary - the CA125 is normal. Additionally, there
are many false positives such as endometriosis, menstruation, pregnancy,
liver disease, or other pelvic infections, which result in a higher CA125
level."
The lack of sensitivity
and specificity is the reason that the CA125 is NOT a good general
screening tool.
CA125 was created to
monitor the effectiveness of chemotherapy and disease progression
in women with cancer. This is its best use.
You deserve the best
monitoring for your health.
About the E-mail "Carolyn's
Story"
You
may be aware of or have received an e-mail with "Carolyn's
story." This e-mail was written in 1998. Now the author
of this e-mail is trying to correct the record. She writes (in
part)
" When
I wrote the original email advocating the CA-125 test for all women every
year, I was not a member of the National Ovarian Cancer Coalition. I had
just had ovarian cancer surgery and two chemotherapy treatments. I knew
very little about ovarian cancer, but I learned that they would have found
my cancer many months earlier if I had been given a CA-125 test. ...
Needless to say, I was upset when I wrote that July 1998 email.
Later, I
learned that the CA-125 test is not always accurate and that cancer
centers and doctors do not recommend it for routine ovarian cancer
screening for that reason.
I have spent
many hours on the internet trying to track down those web sites that have
posted my original email. When successful, I provide them with a more
balanced and informative document."
To read the rest of her response link
to: http://www.breakthechain.org/exclusives/ca125.html
Sources & Added Readings on CA-125:
Misconceptions
About the CA125 Blood Test, CancerWise, Sept 2001.
http://www.cancerwise.org/September_2001/print.cfm
(accessed
Sept 6, 2003)
Tang, Taylor. Questions and Answers
about the CA125. Johns Hopkins University: http://pathology2.jhu.edu/ovca/ca125qa.cfm
(accessed Sept 6, 2003)
University of Texas, MD Anderson:
http://www.cancerwise.org/September_2001/
HS Labs: http://www.bloodworksusa.com/cancer_antigen.html
Other sites reviewing the CA-125:
http://www.snopes.com/toxins/ca125.htm
http://www.medicinenet.com/CA_125/article.htm
Turn page to:
What
screening tests are currently available?
Why
is a vaginal-rectal pelvic exam so important?
Revised: December 01, 2004.
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