THE AUTHORS REPLY

Extract

We thank Delzell (1) for her interest in our recent article (2), in which we reported an association between occupational exposure to organic lead and stomach cancer risk. In her letter, she commented that despite a thorough presentation of the general limitations of our study, 2 specific issues were not discussed in depth.

When addressing the possibility of confounding by other substances, we considered several possible coexposures such as monoaromatic and polyaromatic hydrocarbons, alkanes, solvents, and carbon monoxide. Our data did not demonstrate associations between these substances and stomach cancer. As mentioned by Delzell (1), we did not address possible coexposure and confounding due to exposure to metalworking fluids. She rightfully pointed out that some studies suggest an association between metalworking fluids and stomach cancer (3). However, we do not agree that the study by Zeka et al. (4) was in support of such an association. Because exposure to metalworking fluids was assessed in our study, we have since evaluated the impact of exposure to this group of substances on the associations that we originally reported. Results regarding the association between organic lead exposure and stomach cancer from our original Table 4 (2, p. 1010) remain unchanged. As for our analysis of the separate and joint effects of exposure to organic lead and lead in gasoline emissions on stomach cancer presented in our original Table 6 (2, p. 1011), we observed a negligible increase in risk estimates when comparing cases with population controls and no difference when comparing them with cancer controls. Although metalworking fluids theoretically could have confounded the observed association between organic lead and stomach cancer, our empirical results suggest that it did not occur.