Despite the considerable efforts and funds devoted to cancer research over several decades, cancer still remains a mainly lethal disease. Cancer incidence and mortality have not declined at the same rate as other major causes of death, indicating that primary prevention remains a most valuable approach to decrease mortality. There is general agreement that environmental exposures are variously involved in the causation of the majority of cancer cases and that at least half of all cancers could be avoided by applying existing etiologic knowledge. There is disagreement, however, regarding the proportion of cancer risks attributable to specific etiological factors, including diet, occupation and pollution. Estimates of attributable risks are largely based today on unverified assumptions and the calculation of attributable risks involves taking very unequal evidence of various types of factors and treating them equally. Effective primary prevention resulting in a reduction of cancer risk can be obtained by: (i) a reduction in the number of carcinogens to which humans are exposed; or (ii) a reduction of the exposure levels to carcinogens. Exposure levels that could be seen as sufficiently low when based on single agents, may actually not be safe in the context of the many other concomitant carcinogenic and mutagenic exposures. The list of human carcinogens and of their target organs might be quite different if: (i) epidemiological data were available for a larger proportion of human exposures for which there is experimental evidence of carcinogenicity; (ii) more attention was paid to epidemiological evidence that is suggestive of an exposure-cancer association, but is less than sufficient, particularly in identifying target organs; and (iii) experimental evidence of carcinogenicity, supported by mechanistic considerations, were more fully accepted as predictions of human risk.

Objective-Terbufos is the fourth most commonly used organophosphate insecticide (OP) in the United States. Terbufos has not been demonstrated to be carcinogenic in rodents, although nonarsenical insecticides, including OPs, have been associated with excess cancer in epidemiologic studies. We investigated associations between use of terbufos and incidence of cancer. Methods-TheAgricultural Health Study is a prospective cohort study of 57,310 licensed pesticide applicators from Iowa and North Carolina. Detailed information about 50 pesticides, including terbufos, and potential confounders was obtained from self-administered questionnaires. Terbufos intensity-weighted lifetime exposure-days [(lifetime exposure-days) X (exposure intensity score)]. Cases include all first primary cancers diagnosed between enrollment and December 31, 2005. Hazard ratios (HR) and 95% CI were calculated with Cox proportional hazards models, adjusting for potential confounders.Results-Overall cancer risk was slightly increased among terbufos users (HR 1.21 (1.06-1.37). Suggestive associations were observed between terbufos use and cancers of the prostate (HR highest tertile = 1.21; 95% CI = 0.99-1.47) and lung (HR middle tertile = 1.45; 95% CI = 0.95-2.22) and leukemia (HR middle tertile = 2.38; 95% CI = 1.35-4.21) and non-Hodgkin lymphoma (HR middle tertile = 1.94; 95% CI = 1.16-3.22), although the exposure-response gradients were nonmonotonic and p for trends were not significant. Conclusion-We found suggestive associations between occupational terbufos use and several cancer sites. However, cautious interpretation of these results is warranted by the lack of existing experimental and epidemiologic evidence to support carcinogenic effects of terbufos.

The purpose of this study was to investigate the effect of an imagery training programme on the performance of a soccer task by skilled and novice players. An initial assessment of performance on the soccer task was undertaken, and then 22 skilled and 22 novice players were equally and randomly assigned to either a control or an experimental group. The experimental group was given an imagery training programme consisting of both visual and kinaesthetic imagery, and in which both internal and external imagery perspectives were included. The programme lasted 6 weeks, with the subjects attending bi-weekly sessions of approximately 15 min each. The control group developed a competitive strategy that was totally unrelated to the performance task. Similar to the experimental group, the controls did this over a 6-week period, attending bi-weekly sessions of 15 min duration. Two performance measures were recorded--response time (i.e. the time to complete the soccer task) and performance accuracy (i.e. errors in performing the soccer task recorded in the form of time penalties). Performance on the post-test as measured by response time revealed a significant improvement for both the skilled and novice players in the imagery group. The control group failed to show any such improvement. No effects were found for performance accuracy.

Objective To test whether improvement in household coal stoves affected the incidence of chronic obstructive pulmonary disease (COPD) in Xuanwei County, China. Design Retrospective cohort study (follow-up 1976-92) comparing incidence of COPD between groups with and without chimneys. Participants 20 453 people born into homes with unvented coal stoves;16 606 (81.2%) subsequently changed to stoves with chimneys. Intervention Installation of a chimney in households in which unvented stoves had been used previously. Results Installation of a chimney was associated with distinct reduction in the incidence of COPD. Compared with people who did not have chimneys, the Cox-modelled risk ratio (relative risk) was 0.58 (95% confidence interval 0.49 to 0.70, P < 0.001) in men and 0.75 (0.62 to 0.92, P = 0.005) in women. Modelled risk ratios were robust to different Cox model specifications. Relative risks decreased with time since stove improvement. In both sexes, the reduction in risk became unequivocal about 10 years after stove improvement. Conclusions In Xuanwei, incidence of COPD decreased markedly after household coal stoves were improved.

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