Smoking prevalence remains high (around 60%) among Japanese males, but smok
ing initiation among males born in the 1930s decreased by approximately 10%
due to economic difficulties following World War II. The present study was
designed to examine whether this temporary decline in smoking initiation i
nfluenced the subsequent incidence of lung cancers, especially adenorarcino
ma, Trends of lung cancer incidence by histological type in both sexes were
investigated using data from the population-based cancer registry in Nagas
aki, Japan, from 1986 through 1995, During this period, 5668 males and 2309
females were diagnosed as having lung cancer, and the overall incidence of
lung cancers among both sexes remained stable. However, males aged 55-59 y
ears showed a decrease in the age-specific incidence of adenocarcinoma and
squamous-cell carcinoma (P<0.05 and P<0.01, respectively), In birth cohort
analyses, the incidence of adenocarcinoma and squamous-cell carcinoma was l
ower in the 1935-1939 birth male cohort than in the successive cohorts. The
incidence of lung cancers among females with low smoking prevalence did no
t change with birth cohort. The low smoking initiation among the 1935-1939
birth male cohort appeared to have resulted in a decreased incidence of ade
nocarcinoma and squamous cell carcinoma among middle-aged Japanese males. T
he present study suggests that smoking prevention has an effect in reducing
the incidence of lung adenocarcinoma, as well as squamous-cell carcinoma,
among smokers.