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Cancer that forms in tissues of the oral cavity (the mouth) or the oropharynx (the part of the throat at the back of the mouth) is known as oral cancer.

Oral cancer is part of a group of cancers called head and neck cancers. Oral cancer can develop in any part of the oral cavity or oropharynx. Most oral cancers begin in the tongue and in the floor of the mouth. Almost all oral cancers begin in the flat cells (squamous cells) that cover the surfaces of the mouth, tongue, and lips. These cancers are called squamous cell carcinomas.

Oral cancer is largely a preventable disease with tobacco and alcohol use being the main risk factors. Cancers caused by smoking often take up to 30 years to develop, so tobacco is less likely to be the main reason behind the increase in oral cancer in people in their 40s compared with older people. In addition, since smoking rates have gone down and alcohol consumption has gone up, experts believe the increase in oral cancer rates could mainly be down to drinking.

When oral cancer spreads (metastasizes), it usually travels through the lymphatic system. Cancer cells that enter the lymphatic system are carried along by lymph, a clear, watery fluid. The cancer cells often appear first in nearby lymph nodes in the neck.
Cancer cells can also spread to other parts of the neck, the lungs, and other parts of the body. When this happens, the new tumor has the same kind of abnormal cells as the primary tumor. For example, if oral cancer spreads to the lungs, the cancer cells in the lungs are actually oral cancer cells. The disease is metastatic oral cancer, not lung cancer. It is treated as oral cancer, not lung cancer. Doctors sometimes call the new tumor “distant” or metastatic disease.
Oral cancer is classified according to two criteria:
1.    The cancer location: According to this criterion there are two types of oral cancer:
•    Oral Cavity Cancer: This starts in the mouth, which includes the tongue, lining of the cheeks, gums and teeth, upper or lower jaw, the hard palate (the mouth’s roof), the mouth’s floor (the area beneath the tongue), and salivary glands.
•    Oropharyngeal Cancer: The cancer that starts in the oropharynx, which includes the soft palates (the back of the mouth), the base of the tongue, uvula, and tonsils (one of two small masses of lymphoid tissue located on either side of the throat). Around two-thirds of the oral cancers are found in the mouth, while one-third are found in the pharynx.
2.    The cells where the cancer starts: There are two types of oral cancer:
•    Squamous Cell Carcinoma: This is a type of cancer that starts in the flat cells (called squamous cells) that cover the surface of the oral cavity and orophadynx. Squamous cells carcinoma represents more than 90 percent of all oral cancers. In its early stages, this cancer is confined to the lining layer of the cells and is called carcinoma in situ, but when it extends beyond the lining, it is called invasive squamous cell carcinoma.
•    Minor Salivary Gland Cancer: This is a type of cancer that starts within the salivary glands located in the oral cavity and orophadynx lining tissue. This is a rare type of oral cancer.
Oral cancers may look like open sores or discolored areas in the mouth. The most common signs of oral cancer are ulcers, sores, red or white patches in the mouth that last longer than three weeks and unexplained pain in the mouth or ear. Less common signs include a lump in the neck, a persistent sore throat or difficulty swallowing. If the biopsy shows that cancer is present, the doctor needs to know the stage (extent) of the disease to plan the best treatment. The stage is based on the size of the tumor, whether cancer has spread, and, if so, to what parts of the body. This may involve lab tests and endoscopy. Dental x-rays, chest x-rays, CT scan and MRI can also be conducted.
Treatment of oral cancers is ideally a multidisciplinary approach involving the efforts of surgeons, radiation oncologists, chemotherapy oncologists, dental practitioners, nutritionists, and rehabilitation and restorative specialists. The actual curative treatment modalities are usually surgery and radiation, with chemotherapy added to decrease the possibility of metastasis, to sensitize the malignant cells to radiation, or for those patients who have confirmed distant metastasis of the disease.