Secular trends of nasopharyngeal carcinoma incidence in Singapore, Hong Kong and Los Angeles Chinese populations, 1973-1997.

Nasopharyngeal carcinoma (NPC) is a rare cancer in most parts of world, but rather common in Southern China and Southeast Asia. This study used IARC published datasets to explore the secular trends of incidence rates of NPC among different Chinese populations in Singapore, Hong Kong and Los Angeles, over the time period 1973-1997. We observed great disparity in the risks and time trends of NPC in those selected Chinese populations. The highest risk was in Hong Kong where the incidence rates have declined rapidly throughout the whole study period in both males and females. For Singapore Chinese, the incidence rates also dropped recently in both genders, but the low incidence rates in Los Angeles Chinese have remained essentially unchanged over time. We further assessed the contribution of period and cohort effects to the observed trends in Hong Kong and Singapore populations through age-period-cohort modeling and found that an age-cohort model provided the best fit to the data in both populations, although for Singapore females a simple age-drift model fit the data well. There was a statistically significant decrease in the drop in incidence of NPC for cohorts born around 1940 in Hong Kong and 1958 in Singapore. This indicates that environmental and lifestyle changes play an important role in the declining incidence of NPC over time.