The lack of causality between asbestos and colorectal cancer

To evaluate a potential causal relationship between asbestos exposure and the risk of colorectal cancer, 30 cohort studies published in English were reviewed and analyzed. The latest report of each cohort up through 1993 was used. The outcome measure was the standardized morbidity (incidence) or mortality ratio (SMR). Summary SMRs were examined by type of cohort registration, type of work, type of asbestos, latency from onset of exposure to period of risk, and incidence only. The overall relative risk was 0.99 for all 30 studies. The evidence does not meet the important criteria for a judgment of causality because the relative risk is not consistently elevated, weak in the two studies with a statistically significant elevation of SMR, and limited data do not support a dose-response relationship.