Women who become
infected with multiple strains of the virus linked to
cervical cancer may have a particularly high risk of
developing the disease, new research suggests.
In a study that
followed more than 2,400 Brazilian women, researchers
found that those who became infected with more than one type
of human papillomavirus were far more likely than
women infected with one viral strain to develop
precancerous changes in the cervix.
There are more
than 100 types of HPV, some of which cause genital warts.
Certain strains of genital HPV can cause abnormalities in
the cervical tissue known as "high-grade" lesions,
which can sometimes progress to cancer.
The new findings
suggest that women who become infected with multiple
strains of HPV are at particular risk of developing these
lesions. The results could have implications for
cervical cancer screening and diagnosis, said senior
study author Eduardo Franco of McGill University in
Montreal.
Many experts
already believe that cervical cancer screening could be
improved by routinely running genetic tests to detect
cancer-related HPVs in cervical cell samples, along
with doing standard Pap tests.
Genetic analysis
of HPV types, Franco told Reuters Health, could tell
doctors which women harbor more than one strain and may need
to be followed more closely to catch precancerous
lesions early.
"This is one more
piece of evidence for why we would eventually need to
test for HPV in the general population" as part of cervical
cancer screening, Franco said.
The study, which
is published in the journal Cancer Epidemiology,
Biomarkers & Prevention, included 2,462
women ages 18 to 60 who underwent multiple HPV tests over
four years. The tests were more sophisticated than those
used in clinical practice, which basically give a
"yes" or "no" as to whether a woman has a high-risk
HPV type. They instead specifically identified roughly
40 genital HPV types, including high- and low-risk
types.
At any one test,
Franco's team found, 2% to 3% of the women were infected
with multiple HPV strains. Many
more--22%--tested positive for different
HPV types at some point over the four years. And as a group,
these women were at particular risk of developing
precancerous lesions.
Compared with
women who tested negative for HPV throughout the first year
of the study, those infected with one HPV type were 41 times
more likely to develop high-grade cervical lesions.
But the risk was 92 times greater for women who'd been
infected with two or three HPV types, and more than
400 times higher for those with four to six viral types.
The combination
of HPV-16 and HPV-58 appeared particularly risky, the
researchers found. HPV-16 is one of four viral types
targeted by the recently approved HPV vaccine
Gardasil. The vaccine does not prevent HPV-58
infection, but it would be expected to take away the risk of
"coinfection" with HPV-16, Franco noted.
It's uncertain
why infection with multiple HPV strains raises the odds of
precancerous lesions, Franco said. It could be the direct
effect of the viruses themselves, he explained, but
it's also possible that multiple infections signal a
"faltering of the immune system" in some women, as the
body's defenses are usually able to vanquish HPV. (Reuters)