An abnormal and malignant growth of the cells of the tongue. It usually occurs along the side of the tongue or at the tip. Squamous cell carcinoma is the most common type of cancer. Risk factors include oral human papilloma virus (HPV) infection, overuse of alcohol, smoking tobacco and chewing tobacco. Left untreated the cancer can spread to the gums, lower jaw, lymph nodes, neck, and floor of the mouth.