A skin cancer originating from the basal keratinocytes within the epidermis, usually secondary to DNA damage caused by UV radiations

Aetiology

• Most common malignant skin tumour
• Exposure to UV radiation - the sun-exposed areas of the head and neck are the most commonly involved sites
  • Sun exposure in childhood may be especially important

Risk factors

• Family history or previous history
• Genetic syndromes
  • Naevoid basal cell carcinoma syndrome: autosomal dominant loss of function of the PTCH tumour suppressor gene
  • Xeroderma pigmentosum: defective nucleotide excision repair
  • Oculocutaneous albinism: autosomal recessive absence/defect of tyrosinase resulting in absence of melanin
• Pale skin/light hair - Fitzpatrick type I or II skin
• High levels of sun or UV exposure - for example through occupation, sunburn, or use of sun-beds
• Immunosuppression
• Chronic inflammation, for example at the site of a burn
• Smoking
• Old age and male sex

Pathophysiology

1. Epidermal keratinocyte DNA damaged by solar UV radiation
2. Mutation of tumour suppressor genes and loss of apoptotic function
3. Mutation of protooncogenes
4. Clonal selection of non-apoptosing, mutated cells
5. Solar UV suppresses normal cell mediated immune response agaisnt tumour cells
6. Further growth to macroscopic tumour