Carcinogens in the nose and throat: nasopharyngeal carcinoma in Kenya.

Following the report by Todd (1921), subsequent studies (Digby et al. 1930, Digby et al. 1941, Digby 1951, Hu & Yang 1959) showed nasopharyngeal carcinoma (NPC) to be common in Chinese. Muir (1971) estimated incidence rates for Chinese as 10-20 per 100 000 population annually for males and 5-10 for females, and Ho (1967) has reported an annual incidence of 25.2 per 100 000 for males and 12.4 for females in Hong Kong. Within China the incidence of this disease appears to relate to latitude and these high rates apply only to the South China provinces of Kwantung, Kwangsi and Fukien. Reports from Central and North China indicate that this disease is less prevalent in these areas (Clifford 1970a). Nasopharyngeal carcinoma is rare in the mongoloid peoples of Korea and Japan who are descendants of peoples migrating from the mainland of Asia, mainly Manchuria. For centuries Chinese from South China have migrated and settled throughout the countries of South-east Asia and the Americas. Intermarriage has occurred with the original native inhabitants of these countries. In some instances it has been possible to compare the incidence of NPC in population groups of pure Chinese, mixed Chinese/indigenous, and indigenous stock. In areas such as Singapore, Malaya, Thailand and Indonesia the highest incidences occur in the pure Chinese groups, with rates comparable to but lower than those noted in South China. The lowest rates occur in indigenous native populations and intermediate levels in those with an admixture of Chinese blood (Muir 1971). This association has suggested that the disease may be genetically determined, but this needs reappraisal. Cancer arising as the result of the exposure of a racial group or section of the population to common environmental carcinogens may erroneously be ascribed to an inherited genetic susceptibility. Neither have significant external environmental factors been found affecting these population groups, perhaps because attention has been concentrated almost entirely on the search for carcinogenic inhalants. However, the importance of environmental factors is indicated by analyses of cases by birth in Hawaii, Australia and California which have shown a significantly lower incidence in those Chinese born outside China than in those born in China (reviewed by Clifford 1970a). NPC is rare in the caucasian peoples of Europe, India and America. In populations of European origin the relative frequency of this disease is about 0.3% in males and 0.2% in females. In India and Ceylon this cancer occurs as 0.5% of all cancers. Muir estimates the incidence in occidental countries as less than 1 per 100 000. The occurrence of NPC in Africa has only recently been recognized, though the oldest known pathological specimens are derived from