EXPOSURE TO CROCIDOLITE AND THE INCIDENCE OF DIFFERENT HISTOLOGICAL TYPES OF LUNG-CANCER

Objectives-To estimate the relations between exposure to both tobacco smoke and crocidolite and the incidence of various histological types of lung cancer. Methods-In 1979 all former workers from the Wittenoom asbestos industry who could be traced were sent a questionnaire on smo king history. Of 2928 questionnaires sent, satisfactory replies were r eceived from 2400 men and 149 women. Of the men, 80% had smoked at som e time and 50% still smoked. Occupational exposure to crocidolite was known from employment records and follow up was maintained through dea th and cancer registries in Australia with histological diagnoses obta ined from the relevant State Cancer Registry. Conditional logistic reg ression was used to estimate the effects of tobacco and asbestos expos ure on incidence of different cell types of lung cancer in a nested ca se-control design.Results-Between 1979 and 1990, 71 cases of lung canc er occurred among men in this cohort: 27% squamous cell carcinoma, 31% adenocarcinoma, 18% small cell carcinoma, 11% large cell carcinoma, a nd 13% unclassified or indeterminate. Two of the classified cases and one unclassified case had never smoked. The incidence of both squamous and adenocarcinoma types of lung cancer were greatest in exsmokers an d in those subjects with the highest levels of exposure to crocidolite . After adjustment for smoking habit, the increase in incidence of lun g cancer with increasing exposure to crocidolite was greater for squam ous cell carcinoma than for adenocarcinoma. Conclusions-The results fr om this study have shown significant exposure-response effects for exp osure to crocidolite, and both adenocarcinoma and squamous cell carcin oma of the lung. They also provide some further evidence against the t heory that parenchymal fibrosis induced asbestos is a necessary precur sor asbestos induced lung cancer.