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A pigmented skin lesion

1.  Is this a benign or malignant skin lesion ?
2.  What size excision margins would you take ?

This slide shows a red nodule arising in the centre of a pre-existing pigmented naevus. Any change in size, shape or colour of a naevus should raise the possibility of malignant change. Other symptoms that should cause concern are inflammation, bleeding or altered sensation. This lesion is a superficial spreading malignant melanoma.  The incidence of malignant melanoma is doubling every 10 years and accounts for approximately 1000 deaths annually in the United Kingdom. Public education has increased the number of thin tumours detected but the number of late presenting lesions remains unchanged. 60% of melanomas arise in pre-existing naevi. Risk factors include giant melanocytic naevi, dysplastic naevus syndrome and a history of recurrent sunburn. 10% appears to be inherited as an autosomal dominant disorder with a reduced penetrance.

Four histological types of melanoma are recognised:

  • Superficial spreading melanoma (65%)
  • Nodular melanoma (27%)
  • Lentigo maligna melanoma (7%)
  • Acral lentiginous melanoma (1%)

Superficial spreading melanomas usually occur in middle age and are commonly seen on sun exposed skin - the lower legs of women and the trunk of men. They are usually slightly elevated with variable coloration. Nodular melanomas are aggressive tumours and occur in a slightly younger age group. They are often uniformly coloured with early ulceration and bleeding. Lentigo Maligna is the least aggressive form of melanoma. It is commonly seen on the face of the elderly and presents as a pale brown macule. Its indolent growth and often means that no treatment is required. Acral lentiginous melanoma is the most frequent type seen in Negroes and Orientals occurring on the palms of the hand and soles of the feet. Subungual melanomas are included in this group.

Tumour thickness is the most important prognostic factor for local and distant recurrence and overall survival in melanoma. Tumour thickness is commonly assessed by the Breslow Thickness which is the distance in millimeters from the top of the granular layer of the epidermis to the deepest part of the tumours. The five year survival for tumours <0.75 mm is 95-99%, 0.76-1.49 mm is 80-90%, 1.5-3.99 mm is 60-75%, >4.0 mm is <50%.

Resection margins in melanoma surgery were until recently large and excessive, based on surgical folklore rather than the results of controlled trials. In 1907 Handley recommended in a Hunterian Lecture a resection margin of 5 cm based on the outcome of one single case and this influenced surgical practice for many years to come. The first significant randomised trial was published by the WHO Melanoma Group who randomised over 600 patients with tumours <2mm thick. This showed that resection margins >1cm did not influence survival. It is obviously impossible to predict tumour thickness prior to histological examination but as a guide to clinical practice was suggested by Neades et al (1993) who recommended that impalpable lesions be excised with a margin of 1 cm, palpable lesions 2 cms and frankly nodular lesion 3 cms.

The management of the regional nodes in malignant melanoma is controversial. 20% of clinically palpable nodes are histologically negative. 20% palpably normal nodes have occult metastases. Therapeutic lymph node dissection provides regional control and prognostic information but does not improve survival. Elective lymph node dissection is unnecessary in tumours <0.75 mm as 90% will be cured by local surgery alone. For patients with tumours >4.0 mm 70% will have distant metastases at presentation and lymphadenectomy provides no survival advantage. It should be remembered that lymph node dissection is not without morbidity. About 25% will develop lymphoedema and 25% seromas. The jury remains out on lymphadenectomy for intermediate thickness tumours.

Recent papers

Ball A S, Thomas J. Surgical management of malignant melanoma. Brit Med Bull 1995; 51: 584-608

Neades G T. Safe margins on the excision of primary cutaneous melanoma. Br J Surg 1993; 80: 731-733

O'Rourke M G, Bourke C. Recommended width of excision for primary malignant melanoma. World J Surg 1995; 19: 343-345

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