world cancer report - iarc

SCREENING FOR ORAL CANCER
SUMMARY
> Oral cancer and its precancerous
lesions, including leukoplakia, can be
readily detected by visual inspection of
the oral cavity by trained health workers
and doctors.
> Population screening for oral cancer
results in the diagnosis of large numbers
of oral precancers and an
increased proportion of early stage
tumours. However, a reduction in incidence
of and mortality from oral cancer
resulting from such interventions
remains to be demonstrated.
Oral lesions such as leukoplakia, erythroplakia
and oral submucous fibrosis are
precancerous. A high risk of malignant
transformation of such lesions has been
established in follow-up studies. The proportion
of oral cancers that arise from
pre-existing precancerous lesions is variously
reported in the range of 30-80%.
The natural history of these lesions is not
as extensively documented as that of the
precursors to cervical cancer. Thus, for
example, it is not known whether the different
types of leukoplakia and erythroplakia
constitute a continuum similar to
the different stages evident during the
development of cervical intraepithelial
neoplasia.
Oral leukoplakia refers to uniform, flat,
predominantly white lesions in the lining
of the mouth that cannot be characterized
as any other disease. White lesions
with a smooth, corrugated or wrinkled
surface are referred to as homogeneous
leukoplakia, and those with irregularly flat
or nodular or exophytic white or red and
white lesions are referred to as nonhomogeneous
leukoplakia. Erythroplakia
refers to velvety red, non-removable
lesions in the oral mucosa. Oral submucous
fibrosis is characterized by recur-
172 Prevention and screening
rent inflammation and stiffness of the
oral mucosa with progressive limitation in
opening the mouth and protrusion of the
tongue. In hospital-based studies, a
malignant transformation rate of 44-
17.5% for leukoplakia, and in populationbased
studies rates of 0.13-2.2% over several
years have been reported [1]. The
risk of malignant transformation varies
with sex (higher in females), type and
location of leukoplakia (higher with nonhomogeneous
types and those located on
the tongue or the floor of the mouth),
presence of Candida albicans and presence
of epithelial dysplasia. The proportion
of leukoplakias which regress has
been reported to vary between 5 and 20%
per year. In a subset of 159 individuals
with oral leukoplakia in one oral cancer
screening trial, after three years of followup
the lesions could no longer be detected
in 104 cases (71.2%). It is difficult to
determine to what extent the above findings
are due to variations in case selection
or are a true reflection of the natural
history.
Nature of the intervention
Early oral cancers mostly present as
asymptomatic, small indurated nodules or
thickening or ulceroproliferative growth
(Head and neck cancer, p232). Auxiliary
health care workers can identify the
above early lesions after adequate training
[2]. There are four methods available
for the early detection of oral cancer:
visual examination of the oral cavity by
health professionals, visual examination
after application of toluidine blue, mouth
self-examination and oral cytology.
Visual inspection of the oral cavity by
trained health workers and doctors is the
most widely-evaluated early detection
procedure for oral cancer. Except for an
ongoing randomized intervention trial in
India and the oral cancer screening programme
in Cuba, all other studies are
cross-sectional, mostly in selected clinical
or industrial settings, with the exception
of a few studies in specified general
populations. Very limited information is
available on intermediate and long-term
end-points such as sensitivity and specificity,
stage distribution, fatality rates,
reduction in incidence and mortality.
Evidence of outcome
Oral visual inspection has been shown to
be a sensitive and specific test to detect
oral precancerous lesions and early
asymptomatic oral cancers in several
studies [1-7]. In the population-based
studies, between 1.3 and 7.3% of
screened subjects were referred for fur-
Fig. 4.49 The ingredients of betel-quid include
betel leaf, slaked lime, areca nut and tobacco,
with or without other condiments. Betel chewing
is one of the major causative factors of oral cancer
(together with bidi smoking and alcohol drinking)
in the Indian subcontinent.
Fig. 4.50 Homogeneous oral leukoplakia. This precancerous
lesion can be detected by visual
inspection.