Nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a cancer originating in the nasopharynx, the uppermost region of the pharynx or "throat", where the nasal passages and auditory tubes join the remainder of the upper respiratory tract. NPC differs significantly from other cancers of the head and neck in its occurrence, causes, clinical behavior, and treatment. It is vastly more common in certain regions of East Asia and Africa than elsewhere, with viral, dietary, and genetic factors implicated in its causation.

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Classification

Nasopharyngeal carcinoma is classified as a malignant neoplasm, or cancer, arising from the mucosal epithelium of the nasopharynx, most often within the lateral nasopharyngeal recess or fossa of Rosenmüller. There are three microscopic subtypes of NPC: a well-differentiated keratinizing type, a moderately-differentiated nonkeratinizing type, and an undifferentiated type, which typically contains large numbers of non-cancerous lymphocytes (chronic inflammatory cells), thus giving rise to the name lymphoepithelioma. The undifferentiated form is most common, and is most strongly associated with Epstein-Barr virus infection of the cancerous cells.^[1]

Signs and symptoms

Nasopharyngeal carcinoma produces few symptoms early in its course, with the result that most cases are quite advanced when detected. Once the tumor has expanded from its site of origin in the lateral wall of the nasopharynx, it may obstruct the nasal passages and cause nasal discharge or nosebleed. Obstruction of the auditory tubes may cause chronic ear infections, and patients may experience referred pain to the ear. Metastasis of cancer to the lymph nodes of the neck may also be the first noticeable sign of the disease.^[1]

Causes

Numerous studies have linked common subtypes of NPC to infection with the Epstein-Barr virus (EBV), which has also been implicated in the development of other cancers such as Hodgkin's disease, Burkitt's lymphoma, and HIV-associated lymphomas. There is some evidence that genetic factors, such as HLA type may play a role in the susceptibility of certain ethnic groups to NPC. Finally, dietary risk factors, such as the consumption of salt-cured fish high in nitrosamines, may play a role in the Asian endemic regions. Well-differentiated NPC, with a microscopic appearance most similar to other squamous cell cancers of the head and neck may be more closely associated with the standard risk factors for that disease, such as cigarette smoking.^[1][2]

Treatment

Because NPC occurs in an anatomical site which is poorly accessible to surgeons, and is often advanced at presentation, the most effective means of treatment is generally radiation therapy, either with or without concurrent chemotherapy. While the undifferentiated subtype of NPC is highly radiosensitive, this is less true of the more differentiated subtypes.^[1]

Prognosis

The five-year survival rate of nonkeratinizing and undifferentiated nasopharyngeal carcinomas, with appropriate treatment, is about 65% overall. Cure is highly possible, even when disease has spread to the regional lymph nodes. The prognosis of keratinizing NPC is significantly worse, due to its greater resistance to radiation.^[1]

Epidemiology

NPC is uncommon in the United States and most other nations, but is extremely common in southern regions of China, especially in Taiwan and Guangdong, which accounting for 18% of all cancers in China. While NPC is seen primarily in middle-aged persons in Asia, a high proportion of African cases appear in children. The cause of increased risk for NPC in these endemic regions is not entirely clear.^[1]

References