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Women
from 25 years of age should participate in cervical screening.
This should be within programmes with quality control procedures
in compliance with European Guidelines for Quality Assurance
in Cervical Screening.
In
many developing countries, the uterine cervix is one of the
most prevalent sites for cancer, comprising about 25% of all
female cancers. In industrialised populations, the disease
is less common. In eastern and central European populations,
the annual age-adjusted (using the World Standard Population
as reference) incidence rates for invasive disease are 15–25
per 100.000 women. In the Nordic countries, the annual incidence
was 15–30 per 100.000 women before the start of large-scale
mass screening programmes.
The
effectiveness of screening for cervical cancer has never been
demonstrated in a randomised trial. There is, however, sufficient
non-experimental evidence showing the efficacy of screening
using a cervical smear (Pap) test performed every 3–5
years. This is based on case–control and cohort studies
and on time trends and geographical differences associated
within screening. The largest of these is the collaborative
study co-ordinated by the International
Agency for Research on
Cancer (IARC)
which showed that eradication of the disease is an unrealistic
goal and that maximal protection after a negative smear is
about 90%, which remains roughly the same during several years
after the test. This conclusion is in agreement with the results
of studies on the natural history of the disease, which have
shown that most preinvasive lesions progress to frankly invasive
cancer only over several years.
The
effects are somewhat smaller at a population level. In some
of the Nordic countries, the reduction was about 80% in women
in the age groups exposed most intensively to screening. In
the mid-1980s, after several years of organised screening,
the overall incidence was 5–15 per 100.000 woman-years.
Cervix cancer screening should be offered
to all women over
25 years. There is limited evidence of benefit from screening
in
women aged over 60 years, though the likely yield of screening
is low in women over age 60 since the incidence of high-grade
cervical lesions declines after middle age. Screening this
age
group is associated with potential harms from false-positive
results
and subsequent invasive procedures. Stopping screening in
older
women is probably appropriate among women who have had
three or more consecutive previous (recent) normal Pap smear
results. Yield is also low after hysterectomy, which leaves
some
cervical tissue, and there is scant evidence to suggest that
screening
produces improved health outcomes.
An
organised programme consists of several essential elements.
Defining the population to be screened is important. Personal
invitation is the single most important means of attaining
high attendance, especially when it is combined with effective
information through the mass media. Free service has also
been shown to improve attendance. Quality assurance of all
steps of the process, monitoring and constant evaluation of
the proportion of cancer detected, false positives and false
negative readings, are mandatory. Near maximal effectiveness
is achieved by an organised programme with high coverage,
in which screening is initiated at the age of 25 years and
is repeated at three- or five-year intervals until the age
of 60. Extension of this approach should be considered only
if maximal coverage has been attained, the resources are available
and the marginal cost-effectiveness of the recommended changes
has been evaluated.European Guidelines
for Quality Control in Cervix Cancer Screening have been
developed and are widely followed in Europe.
Infection with certain strains of HPV,
generally acquired sexually,
is the most important risk factor for cervical cancer. With
the
use of (modern) HPV detection methods over 90% of squamous
cell
cervical cancer and 75–85% of high-grade cervical intraepithelial
neoplasia (CIN) lesions have detectable HPV DNA. Given the
implication of HPV infection in cervical cancer, detecting
HPV
could represent an appealing screening method. A study of
2009
women having routine screening in England and Wales, showed
that 44% of CIN lesions of grade 2/3 detected had negative
cytology
and were found only by HPV testing (for types 16, 18, 31 and
33): a further 22% were positive for HPV but demonstrated
only
borderline or mild cytological changes. However, 25% of CIN
grade 2/3 lesions were not detected by the four HPV tests.
Routine
HPV testing for cervical cancer screening is an important
research topic at present as HPV infection is very common
in women less than 30 years old, and what matters are those
women over the age of 30 with a HPV infection that persists
over a long period of time. HPV testing is still to be evaluated
to find the role it could play in cervical cancer screening.
It has the potential to become an important test in detecting
cervix lesions in future and should be a current research
priority.
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