Unexplained cancer clusters: common threads.

A number of identified cancer clusters have followed exposures to mixtures of chemicals. The causes for these cancers could not be attributed to any of the individual chemicals in the mixtures and up to now have remained unexplained. The author presents case studies showing that these previously unexplained cancer clusters have common characteristics. First, they can be attributed to exposures to mixtures that contain at least one lipophilic and one hydrophilic chemical, with octanol:water partition coefficients, K(ow), indicative of lipophilic or hydrophilic character. Second, the specific combinations of lipophiles and hydrophiles act as individual entities and produce cancers not associated with exposure to any of the individual chemicals contained in the mixtures. The cancers that follow these exposures can be in the form of single or multiple cancers per cluster.