Even in the case of a lung malignancy, such as mesothelioma, which is strongly related to asbestos exposure, familial clustering has been reported8,9 and asbestos exposure among some family members could not be proven. While dramatic case reports such as these may offer a striking clinical impression, they do not constitute sufficient evidence for the role of a genetic effect. In particular, rare familial clusters of a disease with such strong environmental influences may simply represent a chance occurrence.