A population-based study of lung cancer incidence trends by histologic type, 1974-81.

All incident cases of microscopically confirmed lung cancer diagnosed between 1974 and 1981 in western Washington State were identified through the Surveillance, Epidemiology, and End Results Program of the National Cancer Institute, Bethesda, MD. The incidence of lung cancer by histologic type was studied in relation to time, with age, sex, and stage of disease at diagnosis being taken into account. Overall and within each sex, the incidence of adenocarcinoma has increased significantly since 1974. The rate of increase has been higher among females (86% increase) than among males (54% increase), with most of the increase in both sexes being among those over age 65 years with distant or unstaged disease at diagnosis. Similar patterns were not observed for squamous cell carcinoma. The potential effects of changes in diagnostic and pathology practice during the study period in producing these results were explored, and etiologic implications of the observed increase in adenocarcinoma were discussed.