Meta-analyses of multiple myeloma and farming.

A series of meta-analyses of peer-reviewed studies of multiple myeloma (MM) and farming were performed, using 32 studies published between 1981 and 1996. Prior to the meta-analyses, all studies were reviewed and evaluated for heterogeneity and publication bias. A random-effects meta-analysis including all of the studies yielded an estimator of relative risk equal to 1.23, with a 95% confidence interval (95% CI) of 1.14, 1.32. The estimator of relative risk obtained from a meta-analysis restricted to female farmers was 1.23 (95% CI = 1.17, 1.29). A third meta-analysis restricted to studies of farmers residing in the central United States resulted in an estimator of relative risk equal to 1.38 (95% CI = 1.27, 1.51). These findings were not influenced by either a publication bias or a specific study design. The consistent significant positive findings suggest that there is an association between MM and farming. Exposures commonly experienced by farmers and that might contribute to the occurrence of MM include infectious microorganisms, solvents and pesticides.