clinico-pathological classification
Last reviewed 07/2022
Malignant melanomas undergo two growth phases - radial and vertical. Vertical invasion is a poor prognostic sign.
Different types may be recognised - Clark (1969):
- superficial spreading (70%)
- nodular (15%)
- lentigo maligna (4-15%)
- acral lentiginous including periungual (5%)
- amelanotic melanoma (1)
Histologically and cytologically, there are several features that distinguish malignant melanomas:
- size:
- most malignant melanomas are greater than 10mm in diameter
- most benign tumours are less than 6mm
- symmetry: malignant lesions are usually asymmetrical with respect to cell type, extension and degree of pigmentation
- ascent of melanocytes: malignant tumours show melanocytes travelling upwards at the lateral margins of the tumour
- epidermal hyperplasia: commonly seen with malignant lesions
- dermal growth:
- malignant melanomas vary in their cell type and architecture in different parts of the tumour
- benign lesions are regular in appearance and change to smaller cells within the depth of the lesion
- cytology: with increasing malignancy, there is a wider variation in cell shape and amount of pigment contained withing the melanocyte
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