Familial Nasopharyngeal Carcinoma 6

6 J. Ma and S. Caoassociated with the genesis of NPC, and a dose–response relationship was demonstrated (Partanen1993). In 1995, formaldehyde was suggested to be anetiological factor for NPC by IARC.Middle-sized (5–10 mm) dust particles are easilyabsorbed to pharynx nasalis. Several epidemiologicalstudies have found that the risk factor for NPC wasincreased in people exposed in wood dust, and it wasdependent on exposure time and dose (Luce et al. 2002).In addition, the risk factor for NPC was reported to beincreased in people exposed to extreme temperatureand work environment with combustibles. However,the exposure ratio for these professional exposures wasrelatively low in most endemic areas, so it cannot beconfirmed whether these factors are independentlyimportant in the high incidence in these areas.1.7.7Chronic Upper Respiratory DiseaseMost epidemiological studies showed that the riskfor NPC was increased by about twofold in peoplewith chronic ear, nose, throat, and upper respiratorydisease (Zheng et al. 1994). It may be due to the conversionof nitrate to nitrite by bacteria present inthese regions, since nitrite is the component of carcinogenN-nitroso.1.7.8Trace ElementNickel is one of the carcinogens to human. Surveysperformed in high-incidence areas found that thecontent of nickel in rice, drinking water, and hair oflocal inhabitants was significantly higher than that inlow-incidence areas. In high-incidence areas, nickelcontent in NPC patients was also higher than inhealthy population. Epidemiological surveys alsofound that trace elements zinc and cadmium werepositively related with the genesis of NPC, whilemagnesium, calcium, and strontium were negativelyrelated (Bolviken et al. 1997).1.8SummaryNPC is a disease with unique epidemiological features.The distribution of the disease demonstrates aclear regional, racial, and gender prevalence. Theincidence of the disease is relatively high amonglocal inhabitants of Southern China, Southeast Asia,Eskimos from the Arctic area, and inhabitants fromNorth Africa and the Middle East, with the highestincidence found in Guangdong province of China,and the incidence in male reaching 20–50/10 5 . NPC isassociated with a number of risk factors. It appearsthat individuals with hereditary susceptibility wereinfected by EBV in the early period of life, then EBVwas activated under the synthetic action of multipleenvironmental factors, and eventually NPC wasdeveloped. In addition to EBV, other environmentalfactors such as trace elements and dietary habits maybe associated with the initiation and development ofthe disease. However, changes in lifestyle in the pastseveral decades in Southern China had little associationwith the etiology of NPC. Further epidemiologicalinvestigations will be needed to detect the changesin the trend of NPC and the underlying risk factors,so that prevention and/or early detection of the diseasecan be realized.ReferencesAlbeck H, et al (1993) Familial clusters of nasopharyngeal carcinomaand salivary gland carcinomas in Greenlandnatives. Cancer 72(1):196–200Armstrong RW, et al (1979) Incidence of nasopharyngeal carcinomain Malaysia, 1968–1977. Br J Cancer 40(4):557–567Bolviken B, Flaten TP, Zheng C (1997) Relations betweennasopharyngeal carcinoma and magnesium and otheralkaline earth elements in soils in China. Med Hypotheses48(1):21–25Buell P (1973) Race and place in the etiology of nasopharyngealcancer: a study based on California death certificates.Int J Cancer 11(2):268–272Burt RD, Vaughan TL, McKnight B (1992) Descriptive epidemiologyand survival analysis of nasopharyngeal carcinomain the United States. Int J Cancer 52(4):549–556Chien YC, et al (2001) Serologic markers of Epstein-Barr virusinfection and nasopharyngeal carcinoma in Taiwanesemen. N Engl J Med 345(26):1877–1882Feng BJ, et al (2002) Genome-wide scan for familial nasopharyngealcarcinoma reveals evidence of linkage to chromosome4. Nat Genet 31(4):395–399Friborg JT, et al (2007) A prospective study of tobacco andalcohol use as risk factors for pharyngeal carcinomas inSingapore Chinese. Cancer 109(6):1183–1191Hildesheim A, et al (1992) Herbal medicine use, Epstein-Barrvirus, and risk of nasopharyngeal carcinoma. Cancer Res52(11):3048–3051Hildesheim A, et al (1995) Cytochrome P4502E1 genetic polymorphismsand risk of nasopharyngeal carcinoma: results