Basis for the review
The extensive epidemiological literature on this topic was reviewed by following searches in the MEDLINE database and bibliographies and citations in articles. Seventy-one peerreviewed cohort studies matched the inclusion criteria: cohort design in settings of mainly occupational exposures to free (raw) asbestos fibers; enumeration of mesothelioma cases; specific information on asbestos fiber types; and latest published reports for cohorts. Cohort epidemiological studies can provide fiber type information, which typically only exists within cohort data sets rather than case control studies. Detailed exposure information is usually obtained for industrial cohort studies. Listed in Tables 1, 2, and 3 are cohort studies found to have sufficient information on the asbestos fiber types. Classification for the studies was based on this reported information unless there was reasonable evidence to indicate that members of the cohort were exposed to mixed fibers. Due to insufficient reports for rates of mesothelioma in cohorts, a formal meta-analysis could not be undertaken.
As seen in the tables, exposure data was provided by two major risk assessment efforts of this decade and other published papers, such as the number of subjects and cases, estimated average exposure levels in short-term samples (fibers/milliliter, milligrams/cubic meter of air, etc.), or cumulative exposures (fibers/milliliter times years of exposure [f/ml-yr]), industries, processes, and fiber types. The time frame for exposures in the tables refers to the ascertained start date of operation of the plant or study period until the end of follow-up of the cohort.