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