Jia et al. BMC Cancer 2010, 10:446 http://www.biomedcentral.com/1471-2407/10/446 culture are responsible for the unusually high incidence of NPC in southern China. In the early 1970 s, Ho suggested that ingestion of salted fish, a traditional southern Chinese food favoured by the Cantonese, might be a cause of the high inci- dence of NPC in the region [11]. Subsequent studies have consistently reported that consumption of salt-pre- served fish in NPC-endemic areas of Guangdong and Guangxi in Southern China [12-14] is strongly asso- ciated with risk of NPC. Consistent results were also observed in Tianjin [15] and Shanghai [16], the areas with low and moderate NPC risk in North and East China respectively. In addition to salted fish, exposure to other preserved food products, such as salted shrimp paste, fermented soybean paste and various types of salted vegetables, is related to NPC risk in Chinese [13,15]. In a current study in Guangxi, a second risk area of Southern China, salted fish consumption was still observed to be related to NPC risk [14]. Herbal medicine is part of traditional Chinese medi- cine. It has been widely used in formal clinical practice in China for many centuries. Although several case-con- trol studies reported a two- to four-fold excess risk of NPC in association with the use of traditional herbal medicines in some Asian populations, no such associa- tion has been reported in southern China. When speci- fic herbal plants were examined, no single plant species appeared to be responsible for the observed association between herbal medicine and NPC. Notably, herbal drugs have also been commonly consumed in the Can- tonese diet as a component of Cantonese-style slow cooked soup and tea. However, until now herbal medi- cines as dietary component have not been evaluated in the context of their potential association with NPC risk. In China, rapid economic development during the past two to three decades has considerably changed the life- style and dietary habits of the Chinese population. These changes have encouraged us to reassess dietary habits and their potential influence on NPC risk in this NPC-endemic area. In Guangdong, a province showing the highest incidence rate in China and different life- styles from adjacent areas, the latest report on dietary factors and their relationship with NPC risk was con- ducted in 1989[13]. With the new biological technology development, it is important and necessary to organize a new epidemiological investigation, in which, we not only focused on lifestyle and other environmental factors, but also collected whole blood samples for each individual so as to develop a systematic genetic study simulta- neously. Base on the project, our new findings of NPC susceptibility genes using GWAS approach have been reported [17]. Gene-environment-EBV interaction on the aetiology of NPC will be investigated in depth in the near future. Page 2 of 7 This study was engaged in re-evaluating previously reported dietary risk factors and in trying to find new potential factors in Guangdong. We observed for the first time that Cantonese herbal tea and herbal slow- cooked soup decrease NPC risk. Methods Subjects This is a hospital-based case-control study. Cases were identified from the medical records of the Sun Yat-Sen University Cancer Center, the largest centre for cancer prevention and treatment in southern China. The centre is located in Guangzhou, the capital of Guangdong pro- vince, and it draws patients from all areas of Guangdong Province. The Sun Yat-Sen University ethical committee approved the study protocol. Eligibility criteria included the following: 1) histological confirmation of NPC, 2) age less than 80 years, 3) no previous diagnosis of or treatment for NPC, and 4) residence in Guangdong pro- vince. Among all eligible NPC patients identified between October 2005 and October 2007. 1387 eligible cases were recruited in the study. A total of 61 patients could not answer the questions qualitatively because of severe side effects associated with radiotherapy. There- fore, 95.8% were enrolled in the study. Controls were frequency-matched to cases by age, sex, education, dialect, household type (rural or urban). The controls were recruited from people who requested health examinations in the centers of physical examina- tion of the largest general hospitals in Guangdong pro- vince. All subjects were required to be Guangdong residents without any history of malignancy. Qualified participants were also required to have the physical and mental ability to complete the interview. A total of 1,459 qualified controls were included in the study. For each participant, we provided services including sero- logic testing for anti-VCA-IgA antibody, otorhinolaryngo- logic examinations, and medical consultations performed by physicians from SYSUCC. Those who were positive for anti-VCA-IgA antibody were referred to the NPC depart- ment at SYSUCC, where they underwent fiberoptic endo- scopy performed by an otorhinolaryngologist. Data collection Interviews were conducted face-to-face by trained inter- viewers employing a structured questionnaire in hospi- tals for case patients and in physical examination centres for control subjects. Informed consent was obtained from each individual before the interview began. Data were collected for demographic characteris- tics (age, gender, education, dialect and household type etc.), lifestyle information and family history of NPC among first degree relatives. Lifestyle information included dietary habits during childhood (defined as