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Health Information
New Strides in Preventing and Detecting
Cervical Cancer: The HPV Vaccine and
Screening Test
On June 8th, the
FDA took a big step toward cervical cancer
prevention by approving
Gardasil, a vaccine
against
human papillomavirus (HPV). Infection
with HPV, which is a common sexually
transmitted virus in both men and women, may
lead to
cervical cancer in women. HPV is
typically benign, causing genital warts or
no symptoms at all, and is easily attacked
by the immune system.
In some cases,
though, the virus remains in a woman’s
cervix, where it can cause precancerous
changes. Gardasil targets four strains of HPV, two of which cause 70% of all cervical
cancers. The vaccine is approved for girls
and women ages 9-26, with the aim of
preventing initial infection; Gardasil
cannot treat an existing infection.
The HPV vaccine
is best used in conjunction with regular
screening, as Gardasil does not protect
against all strains of HPV. In addition,
women already infected with HPV will not
benefit from the vaccine. But which
screening method is best? To answer this
question, a group of Italian researchers
compared three methods of screening cervical
cells for signs of cancer:
-
Conventional Pap test–the sample of
cervical cells is placed on a slide and
examined for precancerous changes
-
Liquid-based Pap test–the sample is
suspended in liquid before being
examined for precancerous changes
- HPV
test–the sample is placed in a liquid
and then tested for the presence of
high-risk strains of HPV
This study, in
the June 7, 2006 issue of the
Journal of the
National Cancer Institute, found that
the HPV test was more sensitive than the
conventional Pap test at detecting
precancerous changes (ie, produced fewer
false negative results), although the HPV
test also resulted in more false positives
than the conventional test.
About the Study
Researchers
based in Turin, Italy recruited more
than 33,000 women, ages 35-60, to take
part in a study comparing three cervical
cancer screening methods. Half of the
women were given a conventional Pap
test, while the other half was screened
with two methods: the liquid-based
Pap
test and an HPV test.
To assess
accuracy, the researchers calculated two
factors: how often the test correctly
identified precancerous cells in the
cervix (sensitivity), and how often the
test correctly identified the absence of
precancerous cells (specificity). Tests
with poor specificity tend to produce
false positive results, which can lead
to unnecessary additional testing and
anxiety.
The HPV
test—which was 41% more sensitive than
the conventional Pap test—was most
likely to correctly identify
precancerous cells. The HPV test
produced more false positives than the
conventional Pap test, but less than the
liquid-based test. When used alone, the
sensitivity of the liquid-based Pap test
was similar to the conventional version.
When used with the HPV test, the liquid
version boosted sensitivity a bit.
However, the liquid-based test was also
most prone to false positives.
The women in
this study were 35 years and older. The
usefulness of the HPV testing in younger
women, among whom HPV infection is more
common, has already been established in
previous studies.
How Does This Affect You?
Now is the
time to talk with your doctor about the
best approach to preventing cervical
cancer for you (and for your daughters).
Women under 26 years old who have not
been infected by HPV are good candidates
for the HPV vaccine. Clinical trials of
21,000 women and teenage girls showed
Gardasil to be safe and 100% effective
in preventing the two most dangerous
strains of HPV. Although these results
are certainly promising, its true safety
and effectiveness will only be known
after its marketing to the public.
In addition,
all women should be screened regularly
with a pelvic exam and either a Pap test
or HPV test. Along with this Italian
study, previous research has pointed to
the HPV test as an equal or better
indicator of cervical cancer than the
conventional Pap test, which remains the
standard of care for cervical cancer
screening in the US.
The main
drawback of the HPV test is its greater
rate of false positives. Researchers
believe that a false positive HPV test
is more likely in women under age 40,
because HPV infection is common in this
age group and usually resolves without
leading to cancer. In women over age 40,
HPV infection is less common and when it
does occur, carries a greater risk of
progressing to cancer. If you are over
age 35 (the cutoff age in this study) or
40, ask your doctor if the HPV test is a
better screening method for you. The
American Cancer Society recommends that
screening begin at age 18 or the onset
of sexual activity, whichever comes
first.
RESOURCES:
American Cancer Society
www.cancer.org
National Cancer Institute–Cervical Cancer
Homepage
www.cancer.gov/cancertopics/types/cervical
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