logo Malignant melanoma

Skin lesions

Malignant melanoma

Objectives

  • Be able to recognise melanoma.
  • Refer pigmented lesions appropriately.

Key points

  • The incidence of melanoma in New Zealand is around 50 per 100,000 and the lifetime risk is estimated to be 1:25.
  • Melanoma is rare in children below the age of 12.
  • Two-thirds of melanoma can be specifically attributed to sun exposure.
  • Those with large numbers of melanocytic naevi and fair skinned individuals who have had repeated sunburns are at increased risk of melanoma.
  • Characteristics of melanoma include change in size and colour over a few months, irregularity of colour within the lesion, and irregularity of outline and surface.
  • Superficial spreading malignant melanoma shows horizontal growth histologically and may be in situ or invasive.
  • Nodular melanoma has a vertical growth pattern. It may be symmetrical, dome-shaped and a single colour.
  • Acral lentiginous melanoma arises on the thickened skin of the soles and palms, and under the nails (subungual melanoma).
  • Lentigo maligna (Hutchinson’s freckle) presents as a slowly enlarging irregularly pigmented lesion on the exposed skin of the older patient and is one type of melanoma in situ.
  • Biopsy of pigmented lesions on the basis of suspicious clinical features requires complete excision with a 2mm margin and pathological examination.
  • Melanoma prognosis mainly depends on the depth of the tumour in mm at the time of excision (Breslow thickness) and level of invasion (Clark’s levels).
  • Melanoma may recur or metastasise locally, in transit to local lymph nodes, in lymph nodes and internally.
  • Ten-year survival rate for melanoma <0.75mm thick is 97.9% but only 40% if it is >4.0mm thick at the time of primary excision.

Introduction

About 1,800 new cases of melanoma are diagnosed each year in New Zealand, with 196 deaths in 1996. The crude incidence was 49.45 (male) and 47.80 (female) per 100,000 in 1995-6 - among the highest in the world, greater than that in Australia. The lifetime risk in the fair skinned New Zealand population is estimated to be 1:25. About 14% of patients with melanoma eventually die of their disease; many deaths occur in young adults.

Prevention

Two-thirds of melanoma can be specifically attributed to sun exposure, particularly to sunburn. Exposure to UVA is thought to be an important risk factor (from sun beds as well as from natural sunlight). Childhood sunlight exposure seems particularly risky.

Lifelong protection from sun exposure should include:

The following features identify high-risk individuals:

Classification of melanoma

Melanoma prognosis mainly depends on the depth of the tumour in mm at the time of excision (Breslow thickness) and level of invasion (Clark’s levels).

The pTNM classification system for stage I and II melanoma is in general use.

Clinical diagnosis

Consider melanoma in all cases of pigmented or changing lesions on the skin in adults. Melanoma is rare in children below the age of 12, but may be impossible to distinguish clinically from Spitz naevus.

Examine the lesion with a good light and magnification.

Clinical evaluation requires:

Characteristics of melanoma:

A Asymmetry of shape and pigment pattern

B Well-defined irregular border

C Variation in colour, often with a red halo

D Diameter over 6mm (but it is possible to diagnose smaller melanomas)

E Elevation (but early melanomas are flat)

These features may miss nodular melanoma (symmetrical, dome-shaped, single colour) and amelanotic melanoma (pink or red without pigmentation).

Biopsy of pigmented lesions on the basis of suspicious clinical features requires complete excision with a 2mm margin. An expert should manage diagnosed melanoma (plastic or general or dermatologic surgeon).

Nodular melanoma

Nodular melanoma shows vertical growth histologically and tends to enlarge more rapidly and deeply than superficial spreading melanoma.

Black nodular melanoma on foot

Amelanotic nodular melanoma on nose

Huge ulcerated nodular melanoma


Superficial spreading melanoma

Superficial spreading malignant melanoma (SSMM) shows horizontal growth histologically and may be in situ or invasive. Generally, the ‘ABCD’ characteristics are helpful for diagnosis.

Typical SSMM

SSMM arising in a fair and freckled 14-year-old girl

Large SSMM mistaken for a bruise

Anal melanoma. Mucosal lesions have a relatively poor prognosis.

SSMM-in situ; faintly pigmented flat lesion on shoulder

Amelanotic melanoma mistaken for superficial basal cell carcinoma


Acral lentiginous melanoma

Acral lentiginous melanoma arises on the thickened skin of the soles and palms, and under the nails (subungual melanoma). It is the predominant melanoma of non-whites.

Acral lentiginous melanoma

Amelanotic destructive subungual melanoma

Widening band of pigmentation characteristic for subungual melanoma


Subungual melanoma

Subungual melanoma is often diagnosed late after the nail has split or been lost. It has a poor prognosis and is treated by amputation of the distal phalanx. It can be difficult to distinguish from haemorrhage, especially if there is no history of trauma. Pigmentation in the skin around the nail is characteristic (Hutchinson’s sign).

Lentigo maligna

Lentigo maligna (Hutchinson’s freckle) is a common pigmented lesion on the exposed skin of the older patient and is considered melanoma in situ. Complete surgical excision is recommended but not always practical. In some cases, careful observation for change is acceptable.

Lightly pigmented lentigo maligna with darker nodular melanoma within it

Longstanding lentigo maligna

Lentigo maligna with amelanotic areas


Histopathological report

Include clinical information including size, colour and duration of the lesion and differential diagnosis. When more than one lesion is excised, make sure all specimens are carefully placed in separate accurately labelled containers.

Acral lentiginous melanoma. Melanoma cells infiltrating up through epidermis. Note thick stratum corneum typical of palms and soles.

Lentigo maligna. Proliferation of abnormal melanocytes along the basal layer of a thinned, sun-damaged epidermis

High power view of melanoma cells. Note mitosis in the centre of the image.


The pathologist’s report should include as a minimum:

Treatment of primary melanoma

The melanoma should be excised completely and diagnosed confirmed by histological examination of the entire specimen, with a clearance of 1 cm for all invasive tumours and deep to fascia. This may require a flap or graft repair to close the wound.

The current recommendations are:

pTisMargin 5mm
pT1, pT2Margin 1cm
pT3Margin 1 to 2 cm
pT4Margin 2 to 3 cm

Melanoma may recur or metastasise locally, in transit to local lymph nodes, in lymph nodes and internally. These areas should be examined at follow-up. About 25% of melanomas 1.5-4mm thick have microscopic lymph node involvement at the time of primary diagnosis, and 60% if >4mm thick. Elective lymph node dissection is not recommended. However, lymphatic mapping and sentinel node biopsy should be considered for melanomas >1mm thick.

Solitary amelanotic melanoma metastasis

Disseminated melanoma

Localised satellite metastases


Survival outcomes

The estimated 10-year survival rates in 1996 according to the South Australian Cancer Registry:

pTisMelanoma in situ100%
pT1Melanoma <0.75mm thick97.9%
pT2Melanoma >0.75mm<1.5mm thick90.7%
pT3aMelanoma >1.5mm <3.0mm thick75.4%
pT3bMelanoma >3.0mm <4.0mm thick55.0%
pT4Melanoma >4.0mm thick40%