Induction of Nasal and Nasopharyngeal Tumours in Sprague-Dawley Rats Fed with Chinese Salted Fish

Epidemiological studies have implied that Chinese salted fish is a human nasopharyngeal carcinogen. In the present study, 162 Sprague-Dawley rats were randomly assigned to one of four experimental groups. Rats in groups 1 (n =41) and 3 (n = 40) were exposed to salted fish from birth through the breast feeding period by giving the maternal rats a diet containing 10% and 5% salted fish, respectively, later feeding the rats with pellets containing 10% and 5% of salted fish respectively. In group 2, the rats (n =41) were given pellets containing 10% of salted fish from 6 weeks of age. Rats in group 4 (n = 40), serving as controls, were only given ordinary pellets. Three rats had nasopharyngeal tumours, 2 from group 1 had a poorly differentiated carcinoma and a squamous cell carcinoma. One rat from group 2 had a squamous cell carcinoma. Four rats had nasal tumours, one fibrosarcoma and one adenocarcinoma were found in rats from group 1. One rhabdomyosarcoma was found in group 2, and one soft tissue sarcoma was found in a rat in group 3. No nasal or nasopharyngeal tumours appeared in the control group. The difference in the occurrence of malignant nasal and nasopharynedl tumours among the four experimental groups was statistically significant (one tailed p for trend = 0.041). The frequency of tumours appearing in other organs such as the breast, kidney, lung, liver and brain was not significantly different between the salted fish treated groups and the control group. Our results support the hypothesis that Chinese salted fish is a nasopharyngeal carcinogen and suggest that Sprague-Dawley rats may be a better animal model for NPC than Wistar rats or Syrian golden hamsters.