For decades women have gone to their gynecologists to get
Pap tests as part of their routine exams. Named for Dr. George Papanicolaou,
who developed it in the late 1920s, the test involves gently collecting cells
from the surface of the cervix and examining them under a microscope to
identify precancerous lesions and early (more curable) cervical cancer. It has
saved millions of women’s lives worldwide.
But might the routine Pap become a thing of the past? In
April the FDA approved the first HPV (human papillomavirus) test, from Roche
Pharmaceuticals, that can be used as a primary screening test. Called the Cobas
HPV test, it analyzes a sample of cells from the cervix (collected in the same
way as for a Pap test) for the presence of any of 14 HPV genotypes that
increase the risk of cervical cancer. Before the FDA approval, HPV testing was
done only in conjunction with the Pap test, not in place of it.
Nearly all cervical cancers are caused by HPV, with two
types responsible for the majority of them. If a woman tests positive for
either of these on the HPV test, it’s recommended that she then have an additional
test called a colposcopy, in which a special magnifying lens is used to
directly examine the cervix (this may also be done following an abnormal Pap
test). If a woman tests positive for any of the 12 other high-risk HPV types,
she should have a Pap test, which would then determine if she needs a
colposcopy. In either case, a positive HPV test does not mean a woman has
cervical cancer, but rather only that she is at elevated risk for it.
The ABCs of HPV
There are many different types of human papillomavirus
(HPV) that are sexually transmitted. Virtually all cervical cancers are caused
by “high-risk” types, with two— types 16 and 18—accounting for about 70 percent
of them and another dozen or so responsible for the rest. (These high-risk
types are also associated with other genital and oral cancers in both men and
women—but they are different from the types of HPV that more frequently cause
genital warts in both men and women.) HPV infection is very common, especially
in young people. In fact, most sexually active people become infected at some
point in their lives. Fortunately, the vast majority of women with HPV do not
develop cervical cancer because the infections are almost always transient—that
is, the body’s immune system tends to clear them within one to two years.
Usually there are no symptoms, and most women never even know they have been
infected. If the infection does persist, however, this could lead to
precancerous changes in the cells of the cervix, which can progress over many
years to invasive cancer.
The goal of screening is to find cervical abnormalities
and treat them before they become a problem. Since the Pap test came into use,
it has greatly reduced the incidence of cervical cancer, especially in
developed countries. But many women are still not being screened, which is
largely why an estimated 12,000 new cases of invasive cervical cancer are still
diagnosed in the U.S. annually and why about 4,000 Americans die from the
disease every year.
In less-developed regions, the numbers are far higher—about
450,000 diagnoses of cervical cancer and 230,000 deaths a year— because Pap
screening rates are far lower there, and where screening occurs, it is often of
poor quality. According to the World Health Organization, HPV testing is a
promising and cost-effective stand-alone screening option in poorer countries
because it requires fewer resources and less training to do than Pap tests.
Safe and effective?
Numerous studies have demonstrated that HPV testing is
more sensitive than cytology (Pap) testing. One study, funded by Roche and
published in the American Journal of Clinical Pathology in 2011, included more
than 47,000 women who had Pap and HPV tests; those who tested positive on
either then had biopsies to confirm the accuracy of the tests. It found that
the HPV test was better than the Pap test in detecting precancerous cells and
reducing the rate of invasive cervical cancer. For example, women with negative
HPV results had a lower risk of developing more severe cervical cell changes
over the next three years than those with negative Pap results.
Another study, in the Lancet earlier this year, combined
data from four large trials with more than 176,000 women ranging in age from 20
to 64. It similarly concluded that HPV screening leads to better detection of—and
thus better protection against—cervical cancer. An advantage of the HPV test is
that the results are fully automated (that is, machine-read); in contrast, the
Pap test relies to varying degrees on the expertise of medical personnel to
detect cell abnormalities.
But the FDA’s decision is controversial. A coalition of
17 groups—including Consumers Union, the National Organization for Women, and
the American Public Health Association—oppose the test as a stand-alone
screening tool because they think its safety and effectiveness have not been
sufficiently tested and that it will cause more confusion for women and their
doctors. Among the concerns, it could lead to overtesting and overtreatment
with more invasive procedures (including more colposcopies and biopsies),
especially in younger women, who are more likely to test positive for HPV but
are at low risk for cervical cancer. Such procedures can have unwanted side
effects, including problems with future pregnancy and delivery.
And what about a woman who persistently tests positive
for the highest-risk HPV types but then has negative results on colposcopy? She
would undergo years of extra surveillance with extra procedures and extra
costs—and extra worry.
Though in most cases it would be covered by insurance,
HPV testing is also about twice as expensive as a Pap test.
Dr. Frank Talamantes, Ph.D,
Professor of Endocrinology (Emeritus)University of California
Santa Cruz, California, 95064
Residence: 83 Sierra Crest Dr.
El Paso, Texas 79902
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