Declining incidence rate of lung adenocarcinoma in the United States

Background: Adenocarcinoma of the lung (ADL) increased worldwide during the last half century. We now report that a continuous decline of ADL began in the United States in 1999. Method: Incidence rates of ADL and squamous cell carcinoma of the lung (SQL) from The Surveillance Epidemiology and End Results Program were reviewed for the 31-year period beginning in 1973. The low-tar cigarette (tar <= 15 mg) consumption/per capita by year was estimated based on cigarette consumption/capita data and the market share of low-tar cigarette of the same year in the United States. Results: From 1973 to 1998, the age-adjusted incidence rate of ADL increased 83% in men, and > 200% in women. From 1999 through 2003, the rate declined 14% in men and 8% in women. An analysis of age-specific incidence rates of ADL according to birth cohort demonstrates that rates declined progressively among persons born after 1934 for both genders. The increase in low-tar cigarette consumption did not precede the increase in ADL incidence rates, and the decline of ADL incidence after 1998 occurred without a preceding decline of low-tar cigarette consumption. Conclusion: Since 1999, the ADL incidence has declined. The temporal trend of ADL incidence may suggest that air pollution could be the possible determining cause for the trend. Increasing use of low-tar cigarettes in the United States and the decline in environmental tobacco smoke may be contributors but are less likely to be the driving force.