INCOME, PERCENT OF WOMEN LIVING IN RURAL- AREAS, PARITY, AND BREAST-CANCER MORTALITY IN SPAIN, 1975-1991

BACKGROUND: The aim of the present study was to analyze breast cancer mortality by provinces in Spain during the period 1975-91, and to asse ss the relationship with the geographical distribution of income level , percent of women living in rural areas and average parity of women i n each province. SUBJECTS AND METHODS: Data were obtained from nationa l statistical sources. Standardized mortality ratios (SMR) for breast cancer were estimated by provinces for the periods 1975-1980, 1981-198 6 and 1987-1991, and for the whole period 1975-1991. Poisson regressio n analysis was used to explore the association between breast cancer m ortality and the above mentioned variables. Provinces were categorized according to the quintile distribution of independent variables, and ecological relative risks were estimated for each category. RESULTS: H igher SMR were observed in island provinces (Canary and Balearic islan d), Catalonia, Basque Country, Navarre and the provinces of Saragosa, Seville and Valencia. Lowest SMR were observed in the inner provinces of Spain and the east part of Andalusian region. This pattern has rema ined very similar along the study period: income level showed a positi ve association with mortality from breast cancer, On the contrary, per cent of women living in rural areas and parity were negatively associa ted to breast cancer mortality. The relative risk estimated for each c hild of parity adjusted by the other factors was 0.92 (95% confidence interval: 0.89-0.94). CONCLUSIONS: The highest mortality from breast c ancer in Spain has been observed in those provinces with the highest i ncome level, the lowest percent of women living in rural areas and the lowest parity. These findings at the ecological (provinces) level are in concordance with results from other studies at the individual leve l, and further supports the hypothesis that for the etiology of breast cancer, environmental factors could play a dominant role.