Melanoma

Background/Epidemiology

• Malignant tumour arising from the melanocytes in the skin
  • Spread via lymph and/or blood
• Incidence ~5-20/100,000/year and rising
  • Not that most patients will have a mole (melacytic naevus) which is benign
• 4 subtypes: superficial spreading, nodular, lentigo maligna and acral lentiginous
• More common in women than men but more men die of it

Risk factors/Aetiology

• Approximately 50% of melanomas arise from a pre-existing naevus.
• There are several lesions which can be considered precursors to melanoma e.g. common acquired naevus (freckle); melanocytic naevus (mole); actinic lentigines
  • Many of theses (or a tendency to freckly), along with type I skin, increases the risk of transformation into melanoma
  • >100 common naevi and >2 atypical naevi (>5mm diameter or on unusual sites e.g. buttocks, scalp, ears, hands/feet) increases the risk dramatically
• UV/Sun overexposure
• Age
• There is a genetic/hereditary component to some degree (familial cases can be associated with genetic traits e.g. tumour suppressor dysfunction of the CDKN2A gene)
• Previous skin cancer

Presentation

• Typically affects the legs in women and the back in men
• Slowly enlarging, macular, pigmented lesion with increasing irregularity in shape and pigment
  • Radial growth phase can last 2 years.  Subsequently, the lesion can become palpable and the vertical growth phase (invasive)
  • NB in nodular melanoma, there is classically a rapidly growing nodule that can bleed/ulcerate which may or may not be deeply pigmented (can be confused with vascular lesions but pigment can usually be visualised using a dermatoscope)
• Features of the lesion
  • 7 point checklist (>=3 suspicious)
    • Major (2 points)
      • Change in size
      • Irregular shape/border
      • Irregular colour
    • Minor (1 point)
      • >6mm in largest diameter
      • Inflammation
      • Oozing or crusting
      • Change in sensation (e.g. itch)
  • ABCDEFG
  1. Asymmetry
  2. Border Irregularity
  3. Colour variation/changes
  4. Diameter >6mm
  5. Elevated or Evolution (i.e. change in characteristics)
  6. Firm
  7. Growth

Diagnosis/Investigations

• Excision biopsy with 2mm margin
  • Breslow thickness/T staging
    • Distance from skin surface
      • T1 <1mm
        • NB in these cases the Clark level should also be documented i.e. what level of skin has been invaded
          • Level 1 is generally in situ melanoma (confined to the epidermis)
          • Level 2- papillary dermis
          • Level 3- reticular dermis
          • Level 4- reticular/deep dermis
          • Level 5- subcutaneous (fat)
      • T2 1-2mm
      • T3 2-4mm
      • T4 >4mm
  • Pathology should also try to identify any lymphovascular invasion and whether there is any ulceration (these are important for prognosis/choice of treatment)
• Sentinal lymph node biopsy
  • Particularly if tumour is ≥1mm deep
• Imaging (chest CT/liver USS/Abdominal CT/PET imaging) can also be done if tumour is ≥1mm, a

Management/Prognosis

• Surgical excision is the primary treatment for locoregional disease (stage I-III i.e. not metastatic disease)
  • Margin depends on breslow staging
    • T1 – 1cm
    • T2 – 1-2cm
    • T3/4 – 2cm
• For metastatic disease,
  • Dacarbazine can be used but response rates are poor and really only improves survival by several months
  • Radiotherapy/surgery can be of limited use for palliation of symptoms caused by metastases
• Prognosis can be estimated using Cochran’s Equation

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