clinico-pathological classification

Last reviewed 01/2020

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