Is the incidence of primary adenocarcinoma of the lung increasing?

Primary carcinoma of the bronchus is a major cause of death in males and females. Several studies report an increase in the incidence of adenocarcinoma and have suggested that this reflects changes in smoking habits or, alternatively, that it is a spurious rise due to changes in diagnostic criteria. To examine the latter suggestion we reviewed three cohorts of bronchial carcinoma from 1970, 1980 and 1990, using immunocytochemical techniques to refine diagnosis. We found that squamous cell carcinoma had been consistently overdiagnosed and adenocarcinoma and adenosquamous carcinoma consistently underdiagnosed in all groups. Also, many tumours showed evidence of divergent differentiation with both squamous and glandular components present. There was a small, but real temporal increase in the proportion of adenocarcinoma over the 10 years between 1970 and 1980, but this was not sustained between 1980 and 1990.