Squamous cell carcinoma on the scalp of an 69 year old man. This form of skin cancer arises from squamous cells, flat scale-like cells in the upper layers of the skin. The tumour forms interconnecting bands of keratinised cells that invade the surrounding tissue. Squamous cell carcinoma is the second most common form of skin cancer. Most cases arise from pre-cancerous lesions known as solar keratosis, which are caused by sun damage. It mostly affects the elderly. Treatment is with surgical removal of the tumour, combined with radiation therapy and chemotherapy.