Trends of lung cancer incidence by histologic type: a population-based study in Osaka, Japan.

We investigated trends of lung cancer incidence from 1974 to 1993 by histologic type, using data from the population-based cancer registry in Osaka, Japan. Since the proportion of cases with histologic types identified was not sufficiently high, sex- and age-specific incidence rates by histologic types were estimated assuming that the distribution of histologic types was the same across the same sex and age group regardless of reporting status. Cumulative risk from 0 to 74 years old for total lung cancer increased 1.3-fold from the period 1974-77 to 1986-89 and then plateaued in the period 1990-93 for both males and females. When divided into histologic types, cumulative risk for incidence of squamous cell carcinoma was almost constant during the study period for both males and females. During the same period, adenocarcinoma increased up to 1.4-fold for both males and females. This increase seemed to have reached a plateau recently for males, but not for females. Small cell carcinoma increased monotonously up to 1.6- to 1.7-fold for both males and females. Large cell carcinoma showed over 2-fold increase for both males and females; however, the estimates fluctuated due to the small number of cases. This study provides further evidence of a relative increase of adenocarcinoma compared to squamous cell carcinoma. Recent trends of tapering increase of lung cancer incidence should be confirmed by further observation.