world cancer report - iarc

Fig. 4.46 Annual numbers of years of life lost as a result of deaths from cervical cancer per 10,000
women, at each year of age, up to age 80, in the absence of screening (dark blue plus light blue). If
screening is implemented, many of these deaths can be prevented; at the peak (age 50), 44 years of life
may be gained per 10,000 women screened (light blue).
tive screening at younger ages or, more
controversially, the possibility that invasive
cancers in young women might be a
rapidly progressing subset of neoplasia
[7].
In contrast to squamous cell carcinoma,
adenocarcinoma of the cervix has no
readily detectable pre-invasive stage.
Therefore, cytological screening would
not be expected to be effective in the control
of this type of cervical cancer [7].
The application of cohort and case-control
studies to the evaluation of screening
effectiveness is complex. Self-selection
for screening by individuals at lower risk
of disease or mortality has been observed
frequently. It is possible that signs or
symptoms led to a cytological smear
being performed, but this may have been
misclassified as a screening test. If differential,
this misclassification would bias
the estimated effect of screening.
Implementation
The major barrier to prevention of cervical
cancer is failure to be screened at all
(Table 4.18). Organized screening is generally
considered to be substantially more
A B C D
efficient than opportunistic screening.
However, there have been few direct comparisons
and the results of these have
been inconsistent. Some reduction in incidence
may be achieved by opportunistic
screening [8].
An estimate of the years of life potentially
saved as a result of screening on the basis
of data has indicated that three-yearly
cytological screening reduces mortality by
91% [9]. This may be an overestimate
because of selection bias. At the age of
50, 44 years of life can be gained per
10,000 women screened. At the ages of
68 and 39, 25 years of life are gained per
10,000 women screened, and at ages 31
and 76, 10 years of life are gained (Fig.
4.46).
Selective screening has been considered.
However, asking women about their sexual
habits is at best difficult, and may be
unacceptable in many societies.
Moreover, it may be difficult to reduce
screening coverage once a programme
aimed at total population coverage is in
place. Another proposal is to cease the
offer of screening to women aged 50 or
more who have had regular negative
smears [10]. It has been suggested that if
a combination of HPV and cytological
testing were introduced in primary
screening, screening could then be
stopped at an earlier age in women negative
on both tests [11].
Considerable variation in the sensitivity
and specificity of cervical cytology smear
tests has been reported [12]. A number of
suggestions for methods to improve cervical
specimen cytology have been made,
with liquid-based cytology techniques currently
receiving most attention. Overall,
Fig. 4.47 Visual inspection of the cervix with 4% acetic acid. In the normal cervix, after the application of acetic acid, no definite acetowhite areas are seen (A).
The visual inspection is declared positive (B) when, after the application of acetic acid, thick, dense, well-defined acetowhite areas develop (arrows). An invasive
cancer is shown before (C) and after (D) the application of acetic acid.
Screening for cervical cancer
169