The anatomy of the oral cavity is particularly challenging because there are many different types of tissue located in this relatively small area. The oral cavity begins at the lips and extends backwards to the front part of the tonsils. Beginning at the front of the upper and lower lips is the very specialized tissue called the vermilion border, which lines the lips. Once inside the mouth, this entire region is coated with a lining that is specialized to provide lubrication of the oral cavity. The bone of the lower jaw called the mandible and of the upper jaw, called the hard palate, are also included in this region as well as the teeth. The lining of the mouth becomes thick overlying this bone. Directly behind the lower teeth is a smooth gutter, known as the floor of mouth. Here, the lower saliva gland empties saliva through specialized ducts just under the tip of the tongue. The front two-thirds of the tongue are also included within the oral cavity. The tongue consists of the specialized thick lining on the top and sides, which contains the taste buds. Underneath this are numerous specialized and coordinated muscles that provide movement of the tongue. The last part of the oral cavity, located in the rear of this region, is the retromolar trigone. This is a firm area just behind the back molars in the lower jaw.
The oral cavity has numerous functions. One function is called oral competence, which is the ability to hold food and saliva in the mouth without drooling. The specialized lining of the mouth as well as the many saliva glands provide lubrication which aide in speech, swallowing and in the digestion of food. The grinding and crushing of food, which occurs in the oral cavity, is also important for digestion. Once foods are prepared for swallowing, the oral cavity helps in swallowing as the tongue and the mouth push the food backward towards the swallowing tube – the esophagus. Finally, our highly coordinated and specialized speech, which is so important to communication, would not be possible without the structures of the oral cavity.
Incidence, Epidemiology and Pathology
Although cancers of the head and neck region only account for five percent of all cancers reported yearly in the human body, 30 percent of these cancers occur in the oral cavity. That is roughly 22,000 new cases per year if cancers of the lip are not included. Between 6000 and 7000 deaths per year occur because of oral cavity cancer. As can be easily seen from the review of the anatomy and functions of this area, cancers of the oral cavity left untreated can have devastating effects on critical life functions for people who have this disease. Similarly, choice of treatment must take into account the potential loss of function in this area.
Cancers of the oral cavity may involve any single one of these specialized types of tissue or more than one. As noted, tissues in this area includes bone, teeth, muscle, nerves, a rich supply blood vessels, numerous saliva gland, and the specialized lining called mucosa. Although tumors may arise in any of these types of tissues they are most commonly related to changes in the lining of the mouth.
The most common cancer of the oral cavity is called squamous cell carcinoma and arises from the lining of the oral cavity. Over 95 percent of oral cavity cancers are squamous cell carcinomas and these cancers are further subdivided by how closely they resemble normal lining cells: well differentiated, moderately differentiated and poorly differentiated. Other types of cancers of the oral cavity include cancers of the salivary glands such as mucoepidermoid carcinoma and adenoid cystic carcinoma, sarcomas (tumors arising from bone, cartilage, fat, fibrous tissue or muscle), and melanomas. The pathologist may also described characteristics of the tumor which make it more concerning such as: deep invasion of the tumor, invasion of nerves, invasion of the lymph vessels, invasion of blood vessels and the presence of multiple separate cancers in the area.
Tobacco and alcohol use are the major risk factors for most cancers of the head and neck including the oral cavity. Although the most common use of tobacco in the United States a cigarette smoking, the use of smokeless tobacco, or chew, is associated with oral cavity cancers. The most common site for oral cavity cancer in the United States is the tongue. In other regions of the world, different areas are more commonly affected. In countries such as India, where the use of a specific type of smokeless tobacco and a substance called beetle nut is common, the inner cheek area of the oral cavity is most commonly affected. Although there has been some decrease in the overall numbers of oral cavity cancers and deaths from the disease noted in the last 20 years, the decrease has not been dramatic.
There are many symptoms that raise concern for the possibility of the oral cavity cancer being present. The most common of these is a nonhealing wound on the tongue, in the floor of mouth or along the inner cheek. These can be painful, but in some cases do not cause significant discomfort. There may be bleeding from the area which occurs in an “on and off” manner. As the lesions increase in size, more symptoms occur. Complaints may include new or increased pain, pain was swallowing, ear pain, a change in speech, uncoordinated swallowing, or a lump in the neck. The most important factor to note is that sores in the mouth, whether they are related to trauma or to a variation of canker sores, should fully heal within three weeks. If this does not occur attention should be sought and trained professional should evaluate this region.
Evaluation and Diagnosis
As part of evaluation for a suspicious area in the oral cavity, usually completed by a specialist in the treatment of diseases of the oral cavity and the head and neck – such as a Head and Neck Surgeon – a thorough history will be taken asking for some of the symptoms noted above. The caregiver may also ask for risk factors including tobacco and alcohol use as well as the family history of cancer. The caregiver will do a thorough physical examination of the area. This will include not only looking at the area suspicious for cancer, but also feeling the area with a gloved finger or an instrument. Examination will usually be done of the entire head and neck region including the throat nose and ears. Particular attention will be given to feeling the neck to note if there are signs of cancer spread to lymph nodes in the neck called metastases. Once the clinical examination is completed, recommendation may be given to obtain a specialized type of X-ray, such as a CT scan or MRI. One or both of these can may be necessary at each can provide very specific information concerning the extent of disease. The physician may also order an X-ray or CT scan of the chest to see if there is any spread of disease to the lungs, the most common site of spread outside of the neck.
At this point, a biopsy – a small piece of tissue taken from the suspected tumor – is often advised. This tissue is sent to a pathologist to define which types of cells are making up the tumor. With tumors of the oral cavity, biopsies can often be done safely in the office. The surgeon may also wish to do the biopsy with the patient under anesthesia. This allows the added benefit of the surgeon being able to better define the size of the tumor and which other tissues may be involved. Evaluation of the entire throat, voicebox, esophagus, and windpipe is also often recommended. The entire procedure is called endoscopy and biopsy. This is done because between 5 and 15% of individuals who have one cancer of the mouth, throat or voicebox may also have another tumor present elsewhere in the head and neck.
Once a full examination has been completed as well as the necessary X-rays and biopsies, the tumor is “staged.” Staging is a well-defined method of describing the exact extent of a specific tumor in an individual patient and then placing that tumor in a specific category. This not only assists in choosing treatment options, but also helps predict how successful therapy will be. There are three categories used to describe the tumor: T (tumor), N (lymph node involvement), M (metastasis – spread to other areas of the body.) This is called the TNM classification system. Tumors of the oral cavity are described by their size. Tumors less than 2 cm are called T1. Tumors greater than 2 cm but less than 4 cm are called T2. Tumors greater than 4 cm are called T3. Any tumor that is deeply invading bone, skin or other areas of the head and neck is labeled T4. Lymph node involvement is labeled as N1 if there is one lymph node less than 3 cm on the same side as the tumor. Lymph node involvement is labeled as N2 if a single lymph node is greater than 3 cm but less than 6 cm, or is on the opposite side of the tumor, or if there are more than one lymph node present. If a lymph node in the neck is greater than 6 cm then it is called N3. The M classification is M0 if there is no evidence of cancer spread elsewhere in the body or labeled as positive if there is evidence of cancer spread to tissues such as the lungs, liver, bones or brain.
Once each part of the TNM classification is completed tumors are then staged into four separate groups: I, II, III, IV. Stages I and II are usually defined as early-stage tumors, whereas stages III and IV are usually defined as advanced stage tumors. Treatment is then based on the stage of the tumor, with more advanced tumors requiring more advanced treatments.
The three main tools for treating cancers of the oral cavity are surgery, radiation therapy, and chemotherapy. For this reason, someone with a cancer of the oral cavity may also meet a specialist from radiation oncology as well as medical oncology. In some cases of advanced cancers of the oral cavity, a specialist in reconstructive surgery may also become involved to assist with specialized reconstruction should it be required.
In general, Stage I and Stage II cancers require one type of treatment, either surgery or radiation therapy, to successfully control the cancer. Advanced Stage III and Stage IV cancers will often require combinations of surgery, radiation therapy and chemotherapy or even the use of all three.
Overall survival rates for any cancer of the oral cavity are about 70 percent five-year survival for stage I or II disease. Five-year survival drops to about 50 percent for stage III cancers and further drops to roughly 35 percent for stage IV cancers.
If surgery is required as part of the treatment of the cancer with in the oral cavity, a major emphasis is placed on providing successful reconstruction. This reconstruction is intended to maintain function as well as appearance. Reconstruction may be as simple as putting the tongue muscles back together in the best possible fashion after the removal of the tongue cancer or the placement of a skin graft to replace the missing oral cavity lining. With more advanced cancers, more advanced reconstruction is required. In such cases, not only is new lining of the oral cavity needed in greater amount, but bone – such as the jawbone – may need to be replaced. In such cases, a surgeon may borrow replacement tissues from elsewhere in the body. Skin and muscle can be moved from the chest to re-build the tongue and mouth. Skin can also be moved from the area of the wrist and used to reline the mouth and read build the tongue. Bone can be moved, with or without skin, from the lower leg, hip or shoulder blade and used to rebuild the upper or lower jaw.
Following the treatment of cancers in the oral cavity with surgery, radiation therapy chemotherapy or combinations of these, several important functions of the oral cavity may be severely affected. These include the lubrication of the mouth and throat, swallowing without choking on foods or liquids, speech and movement in areas where surgery has been done. For this reason, specialists in the rehabilitation of the functions such as speech therapists, swallow therapists, physical therapists and occupational therapists will often be very important in the ultimate goal of curing the patient’s cancer while maintaining an acceptable quality of life. Similarly, specialists in pain management may also be needed to assist with pain.
After treatment of a cancer in the oral cavity has been completed, it will be important to watch not only the area where the cancer originally began but also other areas of the body to make sure there are no signs of the tumor coming back. This is called patient follow-up. The treating physician may request that the patient be seen every 4 to 6 weeks for the first year after treatment to have evaluation for possible signs of regrowth of the original tumor. Such evaluation will include thorough physical exams of the head and neck region: examining the area of the tumor’s original position and examining the neck closely for possible spread to lymph nodes. A chest x-ray and blood tests, such as liver function tests, may also be obtained periodically to check for spread to of cancer to the lungs or liver. Imaging studies such as a CAT scan or MRI may also be obtained periodically to check for any changes that may indicate return of the tumor. These follow-up visits also provide important opportunities for patients to ask their caregivers specific questions concerning persistent symptoms or functional limitations relating to their treatment. Follow-up visits also provide the opportunity for the caregiver to specifically ask questions that may be suspicious for return of the tumor. Such questions include: New ear pain? New pain with swallowing? New difficulty with swallowing or speaking? New weight loss, although you are taking in the same amount of calories? Etc.
As time goes on, the frequency of such follow-up visits will decrease. Because as time goes on tumors are less and less likely to recur. In general, about 70 percent of all the tumors that return after treatment will do so within the first year after the completion of treatment. Ninety percent of the tumors that return after treatment will do so within the first 18 months after treatment. Eventually, follow-up visits may be required once or twice a year. During these visits, the greater concern is not the possibility of the original cancer coming back, but concern for a possible second cancer developing in the head and neck region. This is especially concerning in patients who continue to use tobacco and alcohol after their treatment. If a new cancer (called a second primary cancer) were to occur, it would be important to identify it while it is small and often early-stage to achieve the best cure rate with the least invasive means of treatment. For these reasons, close follow-up after treatment is essential in patients with cancers of the oral cavity.