Geographical differences of cancer incidence in Costa Rica in relation to environmental and occupational pesticide exposure

Background This study describes geographical differences in cancer incidenc e in Costa Rica, and investigates if some of these differences may be relat ed to pesticides. Methods Data were combined from the cancer registry (1981-1993), the 1984 p opulation census, the 1984 agricultural census, and a national pesticide da ta set. The 81 counties of Costa Rica were the units for the ecological ana lyses. Adjacent counties were grouped into 14 regions (3 urban and 11 rural ) with relatively similar socioeconomic characteristics. County indices for population density and agricultural variables were constructed and categor ized. Differences across regions and categories were assessed by comparing observed numbers of incident cases to expected values derived from national rates. Within the tertile of most rural counties, rate ratios between cate gories of high and low pesticide use were calculated. Results In urban regions, excesses were observed for lung, colorectal, brea st, uterus, ovary, prostate, testis, kidney, and bladder cancers; and in ru ral regions for gastric, cervical, penile, and skin cancers. Skin cancers ( lip, melanoma, non-melanocytic skin and penile cancer) occurred in excess i n coffee growing areas with extensive use of paraquat and lead arsenate. In the most rural subset, heavy pesticide use was associated with an increase of cancer incidence overall and at a considerable number of specific sites , including lung cancer (relative risk [RR] 2.0 for men and 2.6 for women) and all female hormone-related cancers (RR between 1.3 and 1.8). Conclusions Regions and populations at high risk for specific cancers were identified. Several hypotheses for associations between pesticides and canc er emerged. The findings call for studies at the individual level.