SERUM CONCENTRATIONS OF PROSTATE-SPECIFIC ANTIGEN AND ITS COMPLEX WITH ALPHA(1)-ANTICHYMOTRYPSIN BEFORE DIAGNOSIS OF PROSTATE-CANCER

Prostate cancer can be detected at an early, potentially curable stage by screening based on digital rectal examination and serum prostate s pecific antigen (PSA). The value of screening appears doubtful, based on high 10-year survival rates in selected cases of early prostate can cer, but this follow-up time may be insufficient. By linking the infor mation on 21172 men who took part in a screening examination in Finlan d, 1968-73, with data from the Finnish Cancer Registry, 44 cases of pr ostate cancer diagnosed up to 1980 were identified. Serum samples from cancer cases and from 74 controls matched for age and time of samplin g were assayed for PSA and its complex with alpha(1)-antichymotrypsin (PSA-ACT). With a cut-off for PSA of 2.5 mu g/L giving 92% specificity , 95% of the cancers developing within the first 5 years, and 52% deve loping in 6-10 years tested positive. As a potential screening test wi th a 5-year interval for men under 65, the sensitivity would be 92% an d specificity 97%. The ratio of PSA-ACT to total PSA was lower in cont rols than in patients wih cancer. Using this ratio, we could eliminate half of the false-positive results in the range 2.5-25 mu g/L without loss of sensitivity. Cancer was typically diagnosed 5-10 years after PSA exceeded 2.5 mu g/L, and the median survival after diagnosis was 3 .6 years. 10-year survivat after drawing the sample was 71% in cancer cases with a PSA concentration less than 4 mu g/L and 48% in those wit h higher concentrations. The corresponding figures at 15 years were 53 % and 27%, and at 20 years 43% and 18%, respectively. These results su ggest it is advisable to confine screening for prostate cancer to men with a life expectancy of clearly more than 10 years-ie, younger men, who have the greatest chance to benefit from early detection.