To evaluate the predictive value of prostate-specific antigen (PSA) in a population-based cohort, the authors analyzed relative survival in all men with localized prostate cancer who were registered in the Swedish National Prostate Cancer Register (NPCR) from 1996 to 2005.
All men aged <75 years with localized tumors were identified in the NPCR. A Poisson regression analysis was performed using observed death as response and the expected death rate as offset. The expected and observed numbers of survivors were calculated with stratification for PSA level and 3 categories of tumor differentiation (Gleason score 2–6, 7, and 8–10). The regression model included PSA as linear splines with a breakpoint at a PSA level of 4 ng/mL and with tumor differentiation as a categoric variable.
The Poisson regression analysis indicated a U-shaped curve for all 3 groups, with a negative correlation between PSA and relative survival in men with PSA levels <4 ng/mL and a positive correlation for men with PSA levels >4 ng/mL. The correlation was significant for all 3 groups, but the negative correlation between PSA and relative survival was significantly more pronounced in the group with Gleason scores from 8 to 10 than in the other 2 Gleason score groups.
The demonstration of an inverse correlation between PSA level and relative survival in the group of men with PSA levels <4 ng/mL indicated the presence of a small but clinically important subgroup with undifferentiated tumors who have cells that have lost the ability to secrete PSA. This group should be taken into consideration when deciding on treatment and when choosing a cutoff level in PSA screening programs. Cancer 2008. © 2007 American Cancer Society.