Time trends of lung cancer incidence by histologic types and smoking prevalence in Hong Kong 1983-2000.

The gender difference in epidemiology of lung cancer has been postulated to be due to the higher susceptibility of women to risk factors especially tobacco smoking. Alternatively, such difference may also be explained by some unknown gender-specific etiological factors, which can have been masked if both the female and male prevalence of smoking are high. Hong Kong has a low female smoking prevalence rate and therefore the trend of the female incidence of lung cancer is particularly interesting because it can reflect the effects of the non-smoking related risk factors more clearly. The present study examined the trends of incidence rates for the major histologic types and smoking prevalence from 1983 to 2000 in Hong Kong with respect to gender. The prevalence of daily smokers decreased from 39.7% in 1982 to 22% in 2000 in males and from 5.6 to 3.5% in females. The time trends of the lung cancer incidence (overall or with respect to age and histology) were similar for both genders. The overall incidence decreased progressively throughout the study period, attributable to the decrease in squamous cell, small cell and large cell carcinoma. The decline occurred in all age groups but to a greater extent in the younger age groups. The incidence of adenocarcinoma increased until 1988-1990 and then stabilized. The initial increase was restricted to the older age groups. These temporal patterns suggested that the same etiological factors affected both genders to a different extent but manifested as similar changes in the direction of incidence over time. To confirm this hypothesis, further studies were needed to clarify the nature of these etiological factors for the non-smoking related lung cancer cases.