world cancer report - iarc

Fig. 5.128 Trends in the incidence of malignant melanoma in New South Wales, Australia.
New South Wales Central Cancer Registry, Australia
on the back, while in women the majority
is on the legs. This difference in site incidence
is not completely explained by differential
exposure to ultraviolet light.
Detection
Melanoma is usually asymptomatic but a
person with melanoma sometimes complains
of an intermittent itch. Pain, bleeding
and ulceration are rare in early
melanoma. A melanoma often arises from
a pre-existing pigmented lesion of the skin
(a mole or “naevus”) but these tumours
can also develop in unblemished skin. The
common predisposing skin lesions are
Fig. 5.129 Intentional sun exposure by holidaymakers
on a beach in Nice, France. The majority of
cases of melanoma is attributable to sporadic,
excessive exposure to ultraviolet radiation which
may clinically manifest as sunburn.
254 Human cancers by organ site
dysplastic naevi, junctional and dermal
naevi and blue naevi. However, the risk for
melanoma development from mature dermal,
junctional and blue naevi is quite
small, estimated at approximately 1 in
200,000. Congenital naevi are also known
precursors of melanoma but the risk for
malignant change is related specifically to
the size of the naevus. Naevi greater than
20 mm in diameter and, in particular, the
large bathing trunk naevi have a high risk
of malignant degeneration. The highest
risk naevus is the dysplastic (atypical)
naevus. These are naevi that are larger
than six mm in diameter, have irregular
Fig. 5.130 Dysplastic naevus syndrome, predisposing
to non-familial malignant melanoma. The
patient shows atypical cutaneous naevi, usually
exceeding 5mm in diameter, with variable pigmentation
and ill defined borders.
pigmentation, an ill-defined margin and
often exist in multiples. Of particular risk
is the dysplastic naevus syndrome (familial
atypical mole syndrome) (Fig. 5.130), in
which the patient may have more than
100 of these irregular naevi; risk is highest
in those patients with dysplastic naevus
syndrome who have a near relative diagnosed
with melanoma.
The clinical features of melanoma are
asymmetry (A), a coastline border (B),
multiple colours and quite often some
areas of blue/black pigmentation (C), and
a diameter greater than six mm (D). As the
melanoma progresses, part or all of the
lesion will become elevated (E) (Figs.
5.131, 5.132). This ABCDE system has
been the basis for clinical diagnosis for
melanoma for many years.
Surface microscopy [4] (dermoscopy, epiluminescence
microscopy) has developed
as an aid to the clinical diagnosis of
melanoma. In this technique, the skin surface
is rendered translucent by the application
of oil and a hand-held instrument
providing magnification of at least ten
times is used to view the internal details of
the tumour. Many additional characteristics,
such as pseudopods, radial streaming,
blue/grey veil, peripheral black dots
and multiple colours are visible and have
been used in diagnostic systems now
readily accessible to the clinician with an
interest in cutaneous diagnosis (Fig.
5.133).
Pathology and genetics
Melanocytes occur primarily in the skin
(where more than 95% of cases of
melanoma occurs) but are also found in
the mucous membranes of the mouth,
nose, anus and vagina and, to a lesser
extent, the intestine; melanocytes are also
present in the conjunctiva, the retina and
the meninges. The morphological classification
system for melanoma defines four
types: superficial spreading melanoma,
nodular melanoma, acral-lentiginous
melanoma, and lentigo maligna melanoma.
However, this classification has been
superseded by a system based on the
histopathological parameters of the
excised lesion. Melanoma is now classified
essentially on the vertical diameter of