Prostate cancer in northern Sweden. Incidence, survival and mortality in relation to tumour grade.

In order to study changes in incidence, survival and mortality of prostate cancer in relation to morphological grade, we analysed all incident cases of prostate cancer in Northern Sweden during three 2-year periods (1974-1975, 1980-1981 and 1986-1987). The age-adjusted incidence increased by 35% from 1974-1975 to 1986-1987, but there was only a minor increase in the mortality rates. The increase in incidence was mainly due to well-differentiated (G1) and moderately differentiated (G2) tumours, whereas the incidence of poorly differentiated (G3) tumours remained stable. The 5-year relative survival rate increased significantly from 1974-1975 to 1986-1987. The relative survival rate for each tumour grade was, however, almost stable over the studied time period. After adjustment for tumour grade the differences in relative survival rate diminished. We believe that the most likely explanation for these changes in incidence, survival and mortality is enhanced detection of tumours with more favourable histology as a result of a more frequent use of the diagnostic tools available.