Urbanization and cancer: changing mortality patterns?

"Analysis of the relationship between cancer rates and urbanization for United States counties for the period 1950-54 reveals the expected urban/rural differences for many digestive, urinary and respiratory organ cancers and for female breast cancer. Similar urban/rural differences existed in many other Western countries. By 1970-75, however, urban/rural differences in the United States had substantially narrowed." It is noted that "available data do not allow formal tests of the relationship between these changes and specific etiological factors, but the data suggest that the spatial convergence is related to the changing geography of such risk factors as smoking, alcohol consumption, manufacturing, and socioeconomic status and to the diminished size and role of the white foreign-born population, as well as to such confounding factors as medical practices and population migration."