Changing patterns of lung cancer incidence by histological type.

Using data from five registries covering 7% of the U.S. population, we investigated lung carcinoma incidence trends from 1969-86 by histological type, sex, race, age, calendar time period, and cohort year of birth. Among white men, squamous cell carcinoma was the most frequent histological type, but by the mid-1980s the age-adjusted rates were decreasing while rates of adenocarcinoma and small (oat) cell carcinoma continued to rise. Among white women, adenocarcinoma was the most frequent type, followed by small cell carcinoma, with rates of all histological types rising over the entire study period. Similar time trends were seen among blacks. Rates for squamous cell carcinoma among both sexes and adenocarcinoma among men, however, were considerably higher for blacks than whites, whereas no racial disparity was seen for small cell carcinomas. Rates for each histological type were higher among men than women, although male-female sex ratios diminished over time. Age-specific rates varied considerably by cohort year of birth; incidence of squamous cell carcinoma among men increased steadily among those born from the late 1800s to the first quarter of this century before declining among those born thereafter. Cohort peaks were also reached, although about 10 to 20 years later, for small cell carcinoma and adenocarcinoma, suggesting an eventual reduction in incidence in these histological types as well. For each type, the peak incidence occurred earlier for men than women. These differing incidence patterns add to the evidence that the mechanisms of lung carcinogenesis may vary by histological type.