Proliferation of atypical melanocytes with potential for dermal invasion and widespread metastases

Aetiology

• Incidence increases with age, but may also affect young people
• About 75% of cutaneous melanomas arise de novo from normal skin, the remainder arising from a pre-existing naevus

Risk factors

• Associated with intermittent intense sun exposure (sunbathing in particular) and sunburn in childhood
• Genetic factors:
  • About 60% of melanomas have an activating BRAF mutation
  • Some acral melanomas have c-kit mutations
  • Rare associations - xeroderma pigmentosum, oculocutaneous albinism
• Other risk factors include fair skin, multiple melanocytic naevi, a family history of melanoma and immunosuppression

Pathophysiology

Types of melanoma

Superficial spreading

• Large, flat, irregularly pigmented lesion
• Commonest in trunk and limbs
• Grows laterally before vertical invasion develops

Acral lentiginous malignant melanomas

• Arise as pigmented lesions on the palm or sole or under the nail, and usually present late

Lentigo maligna melanoma

• Invasive tumour that develops within pre-existing lentigo maligna
• Occurs on sun damaged face/neck/scalp

Nodular malignant melanoma