Mouth cancer cells. Coloured scanning electron micrograph (SEM) of cells from a squamous cell carcinoma (cancer) from a human mouth. The many microvilli (small projections) on the cell's surface and the long filopodia are typical of cancer cells. Squamous cells are a type of epithelial cell that line body cavities, such as the mouth. The main causes of mouth cancer are drinking heavily and smoking. The most common symptom of mouth cancer is an ulcer or sore in the mouth or on the lip that doesn't heal. Treatments used for mouth cancer include surgery, radiotherapy, chemotherapy and targeted therapy. Magnification: x2500 when printed 10 centimetres wide.