Malignant tumour that arises from supra-basal keratinocytes
Aetiology
Associated with lifetime cumulative UV exposure - the most common clinical setting is sun exposed sites, particularly in the elderly
Occasionally arises from chronic leg ulcers, sites of burns (e.g. sinuses - chronic osteomyelitis), chronic lupus vulgaris
Risk factors
Genetic factors: fair skin type, xeroderma pigmentosum, oculocutaneous albinism
Most common skin cancer in the immunosuppressed population
Other risk factors - environmental carcinogens e.g. smoking, ionising radiation (excess x-rays, radiotherapy), trauma
Pathophysiology
Epidermal keratinocyte DNA damaged by solar UV radiation
Mutation of tumour suppressor genes and loss of apoptotic function
Mutation of protooncogenes
Clonal selection of non-apoptosing, mutated cells
Solar UV suppresses normal cell mediated immune response agaisnt tumour cells
Further growth to macroscopic tumour
Growth and spread
Locally invasive
Low but definite risk of metastases
Poor prognosis once metastatic
Clinical features
Warty or hyperkeratotic (crusted) lump or ulcer