Basal cell carcinoma This is usually a slow-growing, locally-invasive, malignant tumour of pluripotential epithelial cells arising from basal epidermis and hair follicles; hence, it affects the pilo-sebaceous skin. EPIDEMIOLOGY The strongest predisposing factor to BCC is UVR. It occurs in the elderly or the middle-aged after excessive sun exposure, with 95% occurring between the ages of 40 and 80 years. The incidence of BCC rises with proximity to the equator, although 33% arise in pas of the body not usually sunexposed. Other predisposing factors include exposure to arsenical compounds, coal tar, aromatic hydrocarbons, ionising radiation and genetic skin cancer syndromes. White- skinned people are almost exclusively affected. BCC is more common in men than women. PATHOGENESIS BCCs have no apparent precursor lesions and their development is propoional to the initial dose of the carcinogen, but not duration of exposure. The most likely model of pathogenesis for BCCs involves mesodermal factors as intrinsic promoters coupled with an initiation step. BCCs metastasise extremely rarely. MACROSCOPIC BCC can be divided into localised (nodular; nodulocystic; cystic; pigmented and naevoid) and generalised (superficial: multifocal and superficial spreading; or infiltrative: morphoeic, ice pick and cicatrizing). Nodular and nodulocystic variants account for 90% of BCC. MICROSCOPIC Twenty-six histological subtypes have been described. The characteristic finding is of ovoid cells in nests with a single 'palisading' layer. It is only the outer layer of cells that actively divide, explaining why tumour growth rates are slower thantheir cell cycle speed would suggest, and why incompletely excised lesions are more aggressive. Morphoeic BCCs synthesize type 4 collagenase and so spread rapidly Ref: Bailey and love 27th edition Pgno : 604