Differential diagnoses: Skin malignancy

Dr Nigel Stollery compares four skin malignancies and offers clues for their diagnosis

Nodular malignant melanoma


  • Malignant tumour of melanocytes
  • More common in fair skin types
  • Genetic component in some cases with a positive family history
  • Two-thirds arise in normal skin, the rest in existing moles
  • ABCDE rule aids diagnosis
  • Survival rates are improving


  • Excision is the mainstay of treatment
  • Prognosis dependent on tumour thickness
  • Research continues, but no curative treatments as yet, except for excision

Nodular basal cell carcinoma


  • Most common skin cancer
  • Often called rodent ulcer, as thought to look like a rat bite
  • More common on sun-exposed areas in fair-skinned individuals
  • Incidence increases with age
  • Usually has a rolled, pearly edge, with central ulceration
  • Slow growing, often over years
  • No metastatic potential


  • Treatment of choice is usually local excision
  • In recurrent cases or large facial lesions, Mohs micrographic surgery can be very helpful
  • In the elderly with large lesions not amenable to surgery, radiotherapy is an alternative

Amelanotic melanoma


  • Malignant tumour of melanocytes
  • Do not make melanin, so lesions are not pigmented
  • Colour usually pink, purple or normal skin colour
  • Diagnosis often late owing to atypical appearance, leading to a poor prognosis
  • Usually have an asymmetrical shape with an irregular border


  • Treatment of choice is surgical excision
  • Metastatic spread can occur, with potential to be fatal

Squamous cell carcinoma


  • Usually occurs on areas of maximum sun exposure
  • Can arise in normal skin, or in lesions such as ulcers
  • May produce keratin, so surface is often scaly or horn-like
  • May ulcerate and bleed
  • Much faster growing than basal cell carcinoma


  • Treatment of choice is surgical excision
  • Potential to metastasise to lymph nodes
  • May be fatal if left untreated
  • Radiotherapy is an alternative if surgery cannot be tolerated

Dr Stollery is a GP in Kibworth, Leicestershire, and clinical assistant in dermatology at Leicester Royal Infirmary

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