Nasopharyngeal carcinoma is one of the most common malignant tumors in China, mostly occurring in southern provinces, with the highest incidence in Guangzhou and eastern Guangxi in particular. Nasopharyngeal cancer can invade the base of skull upward, metastasize to the neck downward, and metastasize to bone, lung, liver and other important tissues and organs with blood flow. Because of the hidden site of nasopharyngeal cancer, important blood vessels and nerves are adjacent to it, and the rate of lymph node metastasis is high, it is impossible to perform whole block resection of primary and cervical metastases. Because most of nasopharyngeal carcinomas are hypofractionated carcinomas, which are more sensitive to radiation, and the primary and cervical metastases can be included in the scope of irradiation at the same time, radiation therapy is currently the first choice of treatment for nasopharyngeal carcinoma.
Epidemiology and etiology】About 80% of nasopharyngeal cancers occur in China, and Guangdong is the most common. The incidence of nasopharyngeal carcinoma is more in Mongolian race and less in other races; it is more in Asian Southwest Pacific countries and less in European and American continent. The age of onset is 30-50 years old, and the incidence in men is 2-3 times that in women. The epidemiological characteristics are as follows: 1) the incidence of nasopharyngeal carcinoma has prominent regional characteristics; 2) the causative factors of nasopharyngeal carcinoma are relatively stable; 3) the age of onset of nasopharyngeal carcinoma cases in China is earlier than other epithelial tumors, and there is also the special phenomenon that adolescent cases are relatively common in medium incidence areas; 4) residents of Guangzhou dialect seem to have higher susceptibility to nasopharyngeal carcinoma.
Nasopharyngeal carcinoma has a rather long precancerous state, and the following can be regarded as a high-risk group for nasopharyngeal carcinoma: 1) those with one of the following conditions: 1) EBV VCA-IgA ≥ 1:80, 2) EBV DNaseAb ≥ 50%, 3) EBV VCA-IgA, EA-IgA, DnaseAb positive in any two of the three, 4) any of the above three sustained titers Those with elevated titer (precancerous state); 2. Any precancerous lesion with moderate or severe proliferation or chemosis of the nasopharyngeal mucosa diagnosed by pathological section examination; 3. Any individual carrying 1P12, 14Q24 fragile sites and 3P14 with significantly increased expression in the high incidence area of nasopharyngeal cancer; 4. Members of high cancer family lines can be considered as a high-risk group with high genetic susceptibility to nasopharyngeal cancer. The etiology is not yet known but may be related to the following factors: ① blood (genetic susceptibility), ② heredity (family predisposition), ③ EBV infection, ④ geographical environment and living habits (regional variability), ⑤ stimulation by certain chemical substances, etc. The pathogenesis may be inferred as follows: the nasopharyngeal epithelial cells, which are genetically susceptible to the action of EBV, are infected with EBV at an early age, and then mutated by one or more synergistic factors in the process of cell reproduction after a number of years in a latent state of infection.
The primary tumor of nasopharynx can be nodular, cauliflower, submucosal, infiltrative, ulcerative, etc., and mostly infiltrates to the deep. Sometimes the primary tumor is very small, but the first presentation is with enlarged cervical lymph nodes or distant metastasis. According to the opinion of the Fifth National Conference on Nasopharyngeal Cancer in 1991, the histological classification of nasopharyngeal mucosa is as follows: ① Highly differentiated squamous carcinoma, accounting for less than 10%, with extensive local infiltration, skull base invasion (upward type), relatively few lymph node metastases, poor sensitivity to radiotherapy and difficult local control; ② Lowly differentiated squamous carcinoma, accounting for 85-90 squamous carcinoma, accounting for 85-90%, including vesicular cell carcinoma, lymph node metastasis is common, sensitive to radiotherapy, with good local control and prognosis; ③ undifferentiated carcinoma, accounting for about 5%, lymph node and distant metastasis are common. The sensitivity of radiation is poor.