Skin cancer cell dividing. Coloured scanning electron micrograph (SEM) of a squamous cell carcinoma cell dividing. The daughter cells are still joined by a cytoplasmic bridge. Cancer cells divide chaotically in an incontrollable manner. They may clump together or spread through the body (metastasis). Squamous cell carcinoma is the second most common form of skin cancer and affects cells in the upper layers of the skin. Most cases arise from pre-cancerous lesions known as solar keratoses, which are caused by sun damage.