Malignant skin tumour, which arises from melanocytes usually in the epidermis.
Commonest skin cancer, rising in incidence.
Median age 50–55 years, rare in children.
Particular problem in Caucasians.
Around 30% of melanomas arise from the junctional component of a preexisting naevus, which has become dysplastic. Excess sun exposure, particularly a history of childhood sunburn, is the major risk factor. Highest incidence in Caucasians with fair skin. Melanomas have a familial tendency and there is recent evidence for the role of tumour suppressor genes.
Most lesions are new lesions not arising in a pre-existing benign naevus. Features suggestive of malignancy include asymmetry, irregular borders, variations in colour in a single lesion and large size. Bleeding, crusting or changes in sensation may also indicate malignant change in a pre-existing lesion.
· Superficial spreading malignant melanoma (70%) occurs anywhere on the body. Lesions are flat with radial growth and microinvasion of the dermis.
· Nodular malignant melanoma (20%) presents as a raised brown-black nodule, although occasionally amelanotic lesions are seen. Tumours grow by vertical extension, the skin lesion may therefore not increase in size.
· Lentigo maligna melanoma (5%) arises from lentigo maligna (a form of intra-epithelial neoplasia). The malignant change is heralded by the appearance of a nodule in lentigo maligna.
· Acral lentiginous malignant melanoma (5%) is confined to hands and nail beds.
American Joint Committee on Cancer (AJCC) staging system:
Stage I: Primary lesions are subdivided according to the thickness of the lesion.
Stage II: Regional nodal spread or satellite lesions within 2 cm of the primary lesion.
Stage III: Fixed metastatic regional lymph nodes or more distal node spread.
Stage IV: Distant metastases.
Primary therapy is wide surgical excision. Lymph node dissection is required if there is evidence of lymph node involvement. Radiotherapy, immunotherapy and chemotherapy are used in metastatic disease.
Prognosis is worse with increasing thickness and stage, and with increasing age and male sex.