Objectives. One of the concerns regarding the widespread use of serum prostate-specific antigen (PSA) as a screening tool for prostate cancer is the possibility that it may detect latent or clinically insignificant cancers. One indicator of clinical importance is thought to be histologic grade, with clinically unimportant cancers more likely to be well differentiated and clinically important tumors more likely to be moderately or poorly differentiated. Methods. Data from the metropolitan Detroit population-based Surveillance, Epidemiology, and End Results Program were examined to determine trends in prostate cancer histologic grading before and after the introduction of PSA screening. Results. From 1989 through 1996, the most recent year for which data are available, a dramatic increase in the incidence of prostate cancer occurred in the Detroit area, corresponding to the routine use of PSA as a screening test for prostate cancer. Local stage cancer demonstrated the largest increase in incidence. The incidence of moderately differentiated cancers also rose substantially during the same period; the incidence of poorly differentiated tumors remained about the same, and the incidence of well differentiated tumors decreased. Coincident with the increasing proportion of moderately differentiated cancers was a significant increase in the proportion of prostate biopsies performed (P = 0.001). Conclusions. These population-based data add important evidence that prostate cancers identified with PSA are more likely to be moderately than well differentiated. Additionally, if the definition of clinical significance depends on histopathologic grade, this finding could further be interpreted as evidence that PSA is more likely to detect clinically significant prostate cancer.
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