Most common form of skin cancer, and also the least malignant, forming a glassy, greyish patch, often with a rim, reminiscent of mother-of-pearl. As it grows it becomes indented in the middle, and ulceration is a possible complication. It occurs most frequently on the face and arms, but there is a form known as carcinoma of the trunk, which looks quite different, usually consisting of large red scaly patches not unlike those produced by psoriasis. The tumour can affect a much greater area than is apparent on the surface, and grows by means of feeler-like excrescences. Metastasis – spread to other parts of the body – can only occur at a very late stage. If an ulcer occurs spontaneously on the skin and does not disappear after the usual treatment, it may well be a rodent ulcer, and the surgeon should remove it in its entirety. To confirm diagnosis tissue removed should be exmined in a laboratory, which will also confirm whether or not it has been completely removed, which is essential.