Epithelial carcinomas of the head and neck arise from the mucosal surfaces in the head and neck area and typically are squamous cell in origin. This category includes tumors of the paranasal sinuses; the oral cavity; and the nasopharynx, oropharynx, hypopharynx, and larynx. Tumors of the salivary glands differ from the more common carcinomas of the head and neck in etiology, histopathology, clinical presentation, and therapy. Thyroid malignancies are described in Chap. 48.
INCIDENCE AND EPIDEMIOLOGY
The number of new cases of head and neck cancers in the United States was 36,540 in 2010, accounting for about 3% of adult malignancies; 7880 people died from the disease. The worldwide incidence exceeds half a million cases annually. In North America and Europe, the tumors usually arise from the oral cavity, oropharynx, or larynx, whereas nasopharyngeal cancer is more commonly seen in the Mediterranean countries and in the Far East.
Alcohol and tobacco use are the most significant risk factors for head and neck cancer in the United States. Smokeless tobacco is an etiologic agent for oral cancers. Other potential carcinogens include marijuana and occupational exposures such as nickel refining, exposure to textile fibers, and woodworking.
Dietary factors may contribute. The incidence of head and neck cancer is higher in people with the lowest consumption of fruits and vegetables. Certain vitamins, including carotenoids, may be protective if included in a balanced diet. Supplements of retinoids such as cis-retinoic acid have not been shown to prevent head and neck cancers (or lung cancer) and may increase the risk in active smokers.
Some head and neck cancers have a viral etiology. Epstein-Barr virus (EBV) infection is frequently associated with nasopharyngeal cancer. Nasopharyngeal cancer occurs endemically in some countries of the Mediterranean and Far East, where EBV antibody titers can be measured to screen high-risk populations. Nasopharyngeal cancer has also been associated with consumption of salted fish.
In Western countries, the human papilloma virus (HPV) is associated with approximately 50% of tumors arising from the oropharynx, i.e., the tonsillar bed and base of tongue. Similar to cervical cancer, HPV 16 and 18 are the commonly associated viral subtypes. The incidence of oropharyngeal cancers is increasing in Western counties. Epidemiologically, HPV-related oropharyngeal cancer occurs in a younger patient population and is associated with increased numbers of sexual partners and oral sexual practices.
No specific risk factors or environmental carcinogens have been identified for salivary gland tumors.
HISTOPATHOLOGY, CARCINOGENESIS, AND MOLECULAR BIOLOGY
Squamous cell head and neck cancers can be divided into well-differentiated, moderately well-differentiated, and poorly differentiated categories. Poorly differentiated tumors have a worse prognosis than well-differentiated tumors. For nasopharyngeal cancers, the less common differentiated squamous cell carcinoma is distinguished from nonkeratinizing and undifferentiated carcinoma (lymphoepithelioma) ...