The evidence for a hypothesis that eating salted fish is associated with nasopharyngeal carcinoma (NPC) is reviewed. The hypothesis was tested among Malaysian Chinese using a matched case-control design. The kinds of salted fish and patterns of use were also investigated in a control group comprising 100 Chinese, 50 Malay and 50 Indian households. During 1980, in Selangor, Malaysia, interviews with 100 Chinese cases of NPC and 100 non-disease controls indicated that salted fish consumption during childhood was a significant risk (relative risk = 3.0, P = 0.04), with an elevated risk for daily as opposed to less frequent consumption. Salted fish consumption during adolescence was a less significant risk, and current consumption not at all. There were 19 kinds of fishes reported as being eaten as salted fish by the 200 control households. There were marked differences between ethnic groups in preference for different kinds: Chinese preferred red snapper (74% of households), Malay jewfish (54%) and Indian red snapper (28%). Salted fish was hardly ever eaten daily by any household; weekly was a moderate frequency in all ethnic groups; less than weekly most common. There were no statistically significant differences between Chinese NPC case and non-disease control participants in kind of salted fish eaten. Results were the same when the data were analyzed by sex, subethnic group and income.
We conducted 2 case-control studies with Malaysian and Hong Kong Chinese and investigated the association between salted fish intake and nasopharyngeal carcinoma (NPC). Both studies show a highly significant association between salted fish intake, especially during childhood, and NPC. Furthermore, from our results we estimate that the majority of NPC cases occurring in the southern Chinese can be attributed to their consumption of this food early in life.
New data are presented concerning the relationship between NPC and HLA antigens among Chinese. When attention is confined to newly diagnosed cases, it can be shown that, apart from the increased risk associated with the joint occurrence of A2 and B-Sin 2, there is also an increased risk associated with BW17 and a decrease in risk associated with A11. Among long-term survivors, however, BW17 is appreciably decreased, whereas A2 in the absence of B-Sin 2 or BW17 is increased. Among Malays, a non-Chinese group, there is an excess among NPC patients of a locus A blank, a blank which is probably associated with the AW19 complex.
Malaysia and Hawaii have several advantages for epidemiologic and laboratory studies on nasopharyngeal carcinoma. Both have multiethnic populations with different incidence rates of nasopharyngeal carcinoma and different life-styles. Malaysia has large populations of Chinese, Malaya, and Indians, and the number of cases of nasopharyngeal carcinoma at any one time is comparatively large. Incidence rates for 1968--72, age-standardized to the World population, for Guangdong hua (Cantonese Chinese) in Malaysia were 24.3/100,000 for males and 12.0/100,000 for females. In Hawaii, the ratio was 12.9/100,000 for males and 6.7/100,000 for females. The small number of cases in Hawaii would require that research in that State be conducted in collaboration with research elsewhere with larger case numbers.
We conducted a case-control study of nasopharyngeal carcinoma among Malaysian Chinese to test inhalants, salted fish consumption, and use of tobacco, alcohol, and nasal ointments as risk factors for the disease. Interviews with 100 cases and 100 controls indicated that salted fish consumption during childhood was a significant risk factor (relative risk, 3.0; p = 0.04); childhood daily consumption of this food item compared to nonconsumption carried a relative risk of 17.4 [95% confidence interval = (2.7, 111.1)]. Occupational exposure to smokes (relative risk, 6.0; p = 0.006) and to dusts (relative risk, 4.0; p less than 0.001) was also significantly associated with nasopharyngeal carcinoma. The two risk factors (consumption of salted fish and exposure to smoke and/or dust) were independent of each other. There was no association between nasopharyngeal carcinoma and tobacco, alcohol, or nasal ointments.
Nasopharyngeal carcinoma (NPC) is commonly found in Southern China and South East Asia. Epstein-Barr virus (EBV) infection is well associated with NPC and has been implicated in its pathogenesis. Moreover, various chromosome rearrangements were reported in NPC. However, the underlying mechanism of chromosome rearrangement remains unclear. Furthermore, the relationship between EBV and chromosome rearrangement with respect to the pathogenesis of NPC has not been established. We hypothesize that during virus- or stress-induced apoptosis, chromosomes are initially cleaved at the base of the chromatin loop domain structure. Upon DNA repair, cell may survive with rearranged chromosomes.