Malignant melanoma

Published on 02/04/2015 by admin

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Last modified 22/04/2025

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194 Malignant melanoma

Instruction

Look at this skin lesion.

Salient features

History

• Age (<50 and location on trunk has better prognosis)

• Family history (a patient with a dysplastic naevus with two relatives having malignant melanoma has a 300 time increased chance of having a malignant melanoma)

• Ask the patient:

• has the mole has changed in colour?
• does the mole itch?
• has it changed in shape/morphology?
• does your skin have freckles or tendency to freckling?
• how may moles does your skin have, greater than 20?
• how may times in your life have you had bad sunburn (with peeling of your skin)?

• Remember MacKie’s four independent risk factors for melanoma: freckles, moles (Fig. 194.1), atypical naevi (Fig. 194.2) and a history of severe sunburn.

image

Fig. 194.1 Mole.

image

Fig. 194.2 The back of an individual with multiple atypical naevi.

Examination

• Irregular and asymmetrical, with a fuzzy border where the pigment appears to be leaking into the surrounding skin (Fig. 194.3). (The American Cancer Society mnemonic to suspect malignancy in a mole is ABCDE: asymmetry, border irregular, colour variegation and diameter >6 mm; elevated lesions are more suspicious.)

image

Fig. 194.3 Mole with pigment that appears to be leaking into surrounding skin.

Proceed as follows:

• Comment if the mole stands out from the patient’s other moles.

• Comment if bleeding and ulceration are present (these are ominous signs).

• Examine regional lymph nodes and the liver (for metastatic spread).

Diagnosis

This patient has a malignant melanoma (lesion) as evidenced by its irregular border and, without delay, biopsy and histological examination must be performed to exclude or confirm the diagnosis.

Questions

What are the different types of malignant melanoma?

Depending on the clinical picture and histological findings these include:

• superficially spreading malignant melanoma (commonest type)

• nodular malignant melanoma

• acral lentiginous melanomas (arising on the palms, soles and nail beds)

• malignant melanoma on mucous membranes

• lentigo maligna melanoma (arising in lentigines in older individuals)

• amelanotic (non-pigmented) melanoma

• miscellaneous: melanoma arising from blue naevi, congenital and giant nevocytic naevi.

Advanced-level questions

What are the patterns of growth of malignant melanoma?

• Radial growth: where the growth is horizontal within the epidermis and superficial dermal layers (e.g. lentigo maligna, acral/mucosal lentiginous, superficial spreading types). During this stage of growth, the tumour does not have the capacity to metastasize.

• Vertical growth: occurs with time, and the melanoma grows downward into the deeper dermal layers as an expansile mass lacking cellular maturation; this correlates with the emergence of a clone of cells with metastatic potential. The nature and extent of this vertical growth phase determines the biological behaviour of malignant melanoma.

What are the predisposing factors?

These include sunlight, the presence of a pre-existing naevus (e.g. dysplastic naevus), hereditary factors.

What is the treatment of such lesions?

Surgery remains the mainstay of treatment and the extent of surgery depends on the thickness of the primary melanoma:

• Excision: following histological examination the area is usually re-excised with margins dictated by the thickness of the tumour

• Elective lymph node dissection is controversial; in general, it is indicated only in melanomas of intermediate thickness with one draining chain of lymph nodes

• Intralesional injection of avirulent herpes simplex virus (but capable of replication) may be of therapeutic benefit in malignant melanoma; this is an experimental therapy (Lancet 2001;357:525)

• Interferon-alfa and vaccine therapy may reduce recurrences.

What are the prognostic factors in these patients?

• Tumour thickness: the deeper the melanoma the more likely is metastasis. Thin melanomas (<0.76 mm) approach 100% cure rate whereas only 20–30% survive for 5 years if the lesion has a depth >1.6 mm

• Level of invasion

• Sex of the patient

• Anatomical location: melanomas in the TANS areas (thorax, upper arms, neck and scalp) show a higher relative risk.

What are melanoma-associated genes?

Candidate genes include:

• the gene for growth regulator p16 on chromosome 9

• CMM1 on chromosome 1p36

• CDK4 on chromosome 12q14, encoding a cyclin-dependent kinase

• rarely, melanoma susceptibility is increased >10-fold by heritable mutations in the genes for the cell cycle regulators CDKN2A and CDK4.

Further reading

1994 N Engl J Med, 331. 1994:163.

Rona Mackie is contemporary professor of dermatology in Glasgow.

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