The B.C.C. is a tumour arising from the cells of the basal layer of the epidermis. The abnormal cells leave their normal position and invade the dermis. It is a relatively innocent cancer, as it does not usually invade blood vessels and spread to distant sites. If left untreated, however, it will quietly spread to the surrounding skin and erode underlying tissues, such as bone. Hence, in the past, these cancers have been called ‘rodent ulcers’.

Causes. Unlike most S.C.Cs, B.C.C.s are not usually preceded by an obvious pre-malignant lesion. Although prolonged sunlight exposure is an important factor in their causation, other factors must be involved also. B.C.C.s are much more common in sunny climates and in light-skinned individuals, and two-thirds occur on the head and neck. However, one-third occur in relatively protected sites, such as on the body, eyelids, and behind the ears. It is therefore thought that regional factors must also be involved.

Features. Patients often describe how they have noticed a spot which, although it is not troubling them, does not go away; it may bleed or crust over, but will never quite heal. The appearances are varied. Most typically, it is a small pearl-like nodule with fine blood vessels overlying it. Sometimes it looks like a very small erosion of the skin, or an ulcer. Overlying it. there may be a small crust. Occasionally it appears like a red scaly plaque with o scalloped margin.

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