Figure
21.6 Falling Mortality Rates with
Cervical Screening and Treatment
CERVICAL SCREENING
The benefits for women of liquid based
cytology
Technological advances are making
screening more accurate and less
stressful for women. By Dr Anne
Szarewski
EXPERT OPINON
Cervical cancer affects approximately
2,800 women in the UK each year, of whom
roughly 1,000 die. The NHS screening
programme was set up in 1988; since
then, women have been invited for
cervical screening at least once every
five years between the ages of 20 and 64
in England and Wales and every three
years between the ages of 20 and 60 in
Scotland.
Cervical cancer is unusual in having a
pre-invasive stage (cervical
intraepithelial neoplasia, or CIN),
which potentially makes it almost
completely preventable by screening. In
the UK, about 200,000 women each year
have an abnormal cervical smear. Between
1987 and 1997, the mortality rate
dropped by about 40 per cent; incidence
has also fallen, from 16 women per
100,000 in 1986 to 9.6 per 100,000 in
2000. A recent paper
estimated that screening saves about
4,500 lives every year.!
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LIQUID BASED CYTOLOGY
One of the main problems with the
conventional smear is that up to 80 per
cent of the cells collected are not
transferred from the spatula to the
slide. In addition, excessive blood and
mucus lead to unsatisfactory smears,
necessitating recall.
In October 2003, it was announced that
liquid based cytology (LBC) would be
introduced in England and Wales
(Scotland already had it). The principle
ofLBC is that instead of smearing the
spatula across a slide, it is rinsed in
a vial of preserving solution. A small
plastic brush is used, because cells
tend to stick to wooden implements. In
the laboratory, the vial is agitated to
distribute the cells evenly, then they
are filtered out under pressure to
produce a thin layer on a slide. One
advantage of this is that the machine
always takes the same number of cells.
The main advantage ofLBC is that it
greatly reduces the number of inadequate
smears; in the UK pilot study, the
inadequate rate fell from 9.1 per cent
with conventional cytology to 1.6 per
cent with LBC.2 Anybody who deals with
women in the screening programme knows
that the anxiety caused by inadequate
smears is enormous and if there were no
other advantages to LBC, it would be
worth introducing for this alone.
Another advantage is that thin layer
cytology is easier to read because there
are no clumps of cells and no blood or
mucus obscuring the view. Screening
times in the laboratory are reduced, so
throughput is increased and results are
made available more quickly.
Studies have also suggested there may be
a reduction in the number of borderline
smears reported and greater detection of
high-grade CIN. However, a recently
published randomised trial conducted in
Italy3 showed no increase in the
sensitivity ofLBC compared with
conventional cytology. There are
conflicting results in different studies
and it is likely that the level of staff
training and quality assurance is
important - it is difficult to show
improvements where the standard is
already very high. It is also apparent
from the pilot studies that there is a
learning curve for LBC. A cost analysis
showed that the reduction in inadequate
smears alone makes LBC cheaper in the
long run than conventional cytology,
although this does not take into account
the considerable start-up costs.
COMPUTERISED SLIDE SCREENING
LBC makes it easier to introduce
computerised slide screening, a major
step forward. In this, a computer is fed
numerous images of normal and abnormal
smears and programmed to draw attention
only to those fields it considers not
completely normal.
Severe dyskaryosis: studies suggest that
liquid based cytology can detect more
high grade CIN than conventional methods
Research has shown that this technology
holds great promise. The computer
identifies 22 fields of interest most
likely to have abnormal cells, which are
then examined by a cytologist.
In the study, LBC slides obtained in a
large population under routine clinical
practice and read using the computerised
system detected significantly more
histological high-grade cervical disease
than conventional cytology slides. A
study based on the same cytologists
showed that the mean time taken to
evaluate and report LBC slides using the
computerised system was 41 minutes per
slide, compared to 10.6 minutes per
slide for conventional cytology.
Another useful aspect of LBC is that the
same sample can be used for other tests,
for example, chlamydia, gonorrhoea and
HPV. This opens up the possibility of
'reflex' HPV testing for triage - if a
woman has a borderline smear, her LBC
sample can be tested for HPV; without
the need for another examination. If'
the HPV test is negative, this would be
reassuring, because it virtually rules
out any possibility of disease. This was
tried in some pilot sites, but a
problem arose because HPV resting gives
many false positives. This approach
still needs some thought, but is another
string to the bow of LBC..
