Trends in incidence of various cancers in Bulgaria, 1981-1990

Bulgaria has undergone considerable social changes in the last 40 years, including a transition from a 75% rural to a 75% urban population. These changes might be expected to be reflected in disease rates. The Bulgarian cancer registry has computerized data on cancer incidence throughout the country from 1981 onwards.

Incidence rates in Bulgaria from 1981 to 1990 of cancers of the lung, stomach, large bowel, prostate and bladder in males and of cancers of the breast, lung, stomach, large bowel, cervix and corpus uteri in females were analysed with particular attention to time trends, age-specific changes in rates and urban/rural differences. Poisson regression was used for statistical analysis.

Male rates of cancers of the lung, large bowel, prostate and bladder increased significantly over the period, with average annual increases of 0.4%, 2.9%, 1.3% and 2.3% respectively. In females, rates of cancers of the breast, cervix and corpus uteri increased significantly, with average annual increases of 1.3%, 1.9%, and 2.9%. In both sexes, stomach cancer incidence declined significantly, by 3.0% per year for males and 3.6% per year for females. Rural rates were lower than urban rates for most cancers, particularly in the higher age groups. The decline in male stomach cancer rates was confined to rural areas. The increases in rates of lung cancer and prostate cancer in males and of colorectal cancer and breast cancer in females were most rapid in urban areas.

Substantial changes in rates of various cancers have taken place from 1981 to 1990, in particular increases in rates of breast cancer and large bowel cancer in women resident in urban areas. It is suggested that dietary changes may be responsible for some of these changes.