Ecological analysis of digestive cancer mortality related to contaminationby diarrhetic shellfish poisoning toxins along the coasts of France

Shellfish consumers are exposed to the risk of diarrhea from, among other c ontaminants, algae that produce diarrhetic shellfish poisoning (DSP) toxins , such as Dinophysis spp. These illnesses have been effectively prevented s ince 1984, when a phycotoxin monitoring network was set up along the coasts of France. There is nonetheless concern that residual levels of okadaic ac id, a known tumor promoter that is the main toxin present in French coastal waters, might increase the risk of cancer among regular shellfish consumer s. To test this hypothesis, we conducted an ecological study linking digest ive cancer mortality rates with a proxy measure of contamination by DSP tox ins in 59 coastal areas. Observed and expected numbers of deaths (using nat ional rates as the reference) were computed by sex, cause of death, and are a for two time periods: 1984-1988 and 1989-1993. The level of contamination in each area was estimated by the total number of weeks since monitoring b egan that production was shut down because of DSP toxin contamination. Usin g both Poisson regressions and test for trends of standardized mortality ra tios across four exposure categories, we found some evidence of association s for several digestive cancer sites (esophagus, stomach, colon, liver, and total digestive cancers for men; stomach and pancreatic cancers for women) . Among men, the only statistically significant result that remained after taking possible confounding by alcohol use into account involved colon canc er. The conclusions provided by this analysis are very tentative; they need to be reproduced and interpreted in the light of additional information on the potential long-term effects of DSP toxins. In the absence of human dat a, they provide some indication of a possible association between exposure to DSP toxins and digestive cancers. (C) 2000 Academic Press.