Scottish cancer mortality: a comparison of urban and rural rates for various tumour locations, 1931–7, and a survey of recent trends

Abstract

1. In order to obtain evidence as to what extent the urban excess in cancer mortality is real, an analysis has been made, in respect of both location of tumour and geographical region, of the cancer mortality statistics for Scotland, 1931–7 inclusive.2. Of the various locations, the greatest urban excess is shown by cancer of the respiratory tract; this is considered to be largely, though probably not entirely, due to better diagnosis and more accurate certification of deaths in the cities. Next come the buccal cavity and uterus; in both these locations certification is likely to be relatively accurate, so that a real excess would seem here to be present. The other accessible locations, the skin and the female breast, do not show significant urban excesses, but the numbers are small, and the existence of a real urban excess is not excluded. The results are in general agreement with those of the English experience 1911–20.3. Further analysis of the data presented by Russell for Scotland, 1923–8, reveals an excess in the industrial counties of deaths for cancer of the buccal cavity, and perhaps a smaller one for cancer of the female breast. These data are, therefore, not inconsistent with our findings.4. As compared with the period 1921–30, the figures for 1931–7 demonstrate, for ages 25–65, a marked improvement in cancer of the buccal cavity and uterus. A recorded fall in cancer of the digestive organs may, in part, be due to more accurate certification in respect of the primary location. The failure of mortality from breast cancer to fall may be due to the same cause. The large increase in lung cancer is almost certainly due, in part, to better diagnosis. For all sites together, the cancer mortality between ages 25 and 65 remained constant for men, and fell by 8% in the case of women. The standardized rate for all ages and both sexes combined increased by 1·3%, a rise which is 2·2 times its standard error.5. The urban excess cannot be entirely explained as due to incomplete certification in the rural areas. The implied effect of social and industrial environment in stimulating tumour growth is in harmony with the known facts regarding occupational and social cancer, and emphasizes the importance which the control of adverse environmental factors may have in the reduction of cancer incidence.