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