Rodent ulcer, a basal cell carcinoma, mimicking an infection or ulcer. Rodent ulcers are the most common form of skin cancer among fair-skinned people, mostly affecting the elderly. The tumour normally appears on the face, and starts as a small, flat nodule that grows slowly into the surrounding tissue, breaking down at the centre to form a shallow ulcer. Fortunately, rodent ulcers seldom spread cancer to other parts of the body. Treatment includes surgical removal, cryosurgery (freezing) and radiotherapy.