Lung cancer incidence in Australia: impact of filter-tip cigarettes with unchanged tar yields.
Blizzard L., Dwyer T.
Filter-tip cigarettes became popular in Australia in the late 1950s, but "tar" yields remained high for another decade. Because of this, the effect of filters independently of tar reductions can be estimated by comparing the age-adjusted incidence of lung cancer for relevant birth cohorts of Australians. Separate analyses by histologic type may throw some light on the specific effects of filters. Age-adjusted incidence of squamous cell carcinoma (SCC), small cell lung carcinoma (SCLC) and adenocarcinoma (AC) was estimated by Poisson regression for 5-year birth cohorts of Australians using lung cancer registration data for 1982-95. To take account of changes in smoking prevalence, ever-smoker less never-smoker differences in age-adjusted incidence were estimated. Comparisons were made for smokers born during 1930-34 and 1940-44. Smokers born in 1940-44 commenced smoking at the time of introduction of filter-tips. Age-adjusted incidence of SCC (-23%) and SCLC (-21%) but not AC (+7%) was lower for female smokers born during 1940-44. For male smokers, rates of SCC (-42%), SCLC (-43%) and AC (-24%) were each lower. The high rates overall of 1940s-born women were due to disproportionately higher incidence of AC, the type that comprised 42% of diagnoses with histologic confirmation. In Australia, the switch to filter-tip cigarettes prior to any reduction in tar yields was associated with reduced incidence of SCC and SCLC, and of AC for men only. Rates of AC were not reduced for women, indicating that other factors were important for this type of lung cancer.