الفهرس 
EPIDEMIOLOGY AND ETIOLOGY OF NASOPHARYNGEAL CARCINOMAOnly 14 pages are availabe for public view
 |  | from | 292 |  |  |
| | | from | 292 | | |
Abstract
N
asopharyngeal carcinoma is the 23rd most common cancer in the world. Nasopharyngeal carcinoma (NPC) is a rare disease in the United States, however, the incidence rates are much higher in Asia.
Nasopharyngeal carcinoma (NPC) has a unique and complex etiology that is not completely understood.Well-established risk factors for NPC include elevated antibody titers against the Epstein-Barr virus, consumption of salt-preserved fish, a family history of NPC, and certain human leukocyte antigen class I genotypes.
The World Health Organization defines NPC as a carcinoma arising in the nasopharyngeal mucosa that exhibits light-microscopic or ultrastructural evidence of squamous differentiation The World Health Organization (WHO) has classified NPC into 3 categories. WHO-1 is defined as well–to–moderately differentiated squamous or transitional cell carcinoma with keratin production. WHO-2 is nonkeratinizing carcinoma. WHO-3 is undifferentiated carcinoma, including lymphoepithelioma.
NPC is notoriously difficult to diagnose. A neck mass is consistently one of the most common presentations, and, unfortunately, is a sign of advanced disease. Cranial nerve deficits are also common. Diagnosis is made by biopsy of the nasopharyngeal mass. Work-up includes careful visual examination (by mirror or endoscopic examination); documentation of the size and location of the tumor and neck nodes; evaluation of cranial nerve function and hearing; skull films (especially base of skull views) and evaluatin of neural foramina.
Radiation therapy has been the standard of care in patients with NPC for several decades. High-dose radiation therapy is the primary treatment, both for the primary tumor site and the neck. Surgery is usually reserved for nodes that fail to regress after irradiation or for nodes that reappear after an apparently complete clinical response. Radiation therapy is used to treat the main nasopharyngeal mass and nearby lymph nodes. In Stages 0 and I nasopharyngeal cancer the usual treatment is radiation therapy only, while In Stages II, III and IV nasopharyngeal cancer patients usually receive chemotherapy with cisplatin and sometimes another drug along with radiation therapy.
Up to the early 1990s, radical radiotherapy for NPC was delivered by two-dimensional (2D) techniques.The conventional practice had been to deliver tumoricidal radiation doses (total 60–70 Gy;1.8-2 gy per fraction in a 6–7 week course) to anatomical structures at risk of tumor invasion in the vicinity of the nasopharynx by two lateral opposing fields or multiple fields.