Incidence of lung cancer by histological type from a population-based registry

Using data from a population-based registry, the Cancer Surveillance Program of Orange County, we examined patterns in lung cancer incidence by histological type for 1984 in Orange County, CA. Age-adjusted incidence rates per 100,000 population are 66.4 for men and 34.1 for women. Compared to 1983 rates for whites from all SEER areas combined, Orange County incidence rates are lower for men but equal for women. Squamous cell carcinoma incidence shows a strong male predominance [male/female 3.4; 95% confidence interval = (2.6, 4.4)], whereas the male/female incidence ratios for adenocarcinoma [male/female 1.4; 95% confidence interval = (1.1, 1.8)] and small cell carcinoma [male/female = 1.8; 95% confidence interval = 1.3, 2.4)] are closer to unity. Smoking habits were abstracted from medical records for 79% of cases. Only 8% of lung cancer cases (5% of men and 12% of women) with known smoking habits are nonsmokers. Adenocarcinoma is the most common cell type among women smokers and nonsmokers, while squamous cell carcinoma predominates in both male smokers and nonsmokers. Cases who smoked were younger at diagnosis than nonsmokers (P less than 0.001) for each cell type. Despite a greater proportion of nonsmokers, cases with adenocarcinoma were younger at diagnosis compared to small cell carcinoma (P less than 0.01) and squamous cell carcinoma (P less than 0.05). The observed patterns of incidence rates by histological type are not entirely explained by current knowledge of the relationship between smoking and cell type.