Environmental factors in the etiology of nasopharyngeal carcinoma: report on a case-control study in Hong Kong.

A case-control study was undertaken of Cantonese NPC patients hospitalized in the Queen Elizabeth Hospital, Hong Kong. One age- and sex-matched control was selected for each NPC case from hospitalized patients with cancers other than NPC. A total of 150 NPC patients and 150 controls were interviewed in order to compare the two groups with respect to socio-economic status, dietary habits and health status. In addition to the individual patients and controls, healthy members of their respective households were also interviewed, in order to obtain information not influenced by the experience of having cancer. Weaning habits were compared in the households of NPC patients and those of controls by asking women who had ever breast fed a child about food supplements they had given to the baby during, and immediately after, weaning. The following factors were found to be positively associated with NPC: (1) belonging to the four lowest occupational classes; (2) practicing Buddhism or ancestor worship and having religious altars in the house; and (3) having a history of previous illnesses of the ear or nose after the age of 15 years. The following factors were found to be negatively associated with NPC: (1) eating of bread; (2) eating of tinned food; and (3) use of spices. The study of weaning habits disclosed that salted fish was given to babies just after weaning more often in households with an NPC case than in control households. A multivariate analysis showed that traditional lifestyle and the consumption of salted fish during weaning are independent risk factors for NPC. This analysis also revealed that two or three of the many expressions of a traditional lifestyle included in the study could account for the total increase in NPC risk associated with this way of life, although it is quite possible that other, as yet unidentified, factors are just as important.