Summary of First Four Prostate, Lung, Colorectal, and Ovarian Screening Roundsa continued...
In an examination of trends of prostate cancer detection and diagnosis among 140,936 white and 15,662 African American men diagnosed with prostate cancer between 1973 and 1994 in the National Cancer Institute's Surveillance, Epidemiology, and End Results (SEER) database, substantial changes were found beginning in the late 1980s as use of PSA diffused through the United States; age at diagnosis fell, stage of disease at diagnosis decreased, and most tumors were noted to be moderately differentiated. For African American men, however, a larger proportion of tumors were poorly differentiated.
Since the outset of PSA screening beginning around 1988, incidence rates initially rose dramatically and fell, presumably as the fraction of the population undergoing their first PSA screening initially rose and subsequently fell. There has also been an observed decrease in mortality rates. In Olmsted County, Minnesota, age-adjusted prostate cancer mortality rates increased from 25.8 per 100,000 men from 1980 to 1984 to a peak of 34 per 100,000 from 1989 to 1992; rates subsequently decreased to 19.4 per 100,000 from 1993 to 1997. Similar observations have been made elsewhere in the world,[94,95] leading some to hypothesize that the mortality decline is related to PSA testing. In Quebec, Canada, however, examinations of the association between the size of the rise in incidence rates (1989–1993) and the size of the decrease in mortality rates (1995–1999), by birth cohort and residential grouping, showed no correlation between these two variables. This study suggests that, at least during this time frame, the decline in mortality is not related to widespread PSA testing.
Cause-of-death misclassification has also been studied as a possible explanation for changes in prostate cancer mortality. A relatively fixed rate was found at which individuals who have been diagnosed with prostate cancer are mislabeled as dying from prostate cancer. As such, the substantial increase in prostate cancer diagnoses in the late 1980s and early 1990s would then explain the increased rate of prostate cancer death during those years. As the rate of prostate cancer diagnosis fell in the early 1990s, this reduced rate of mislabeling death due to prostate cancer would fall, as would the overall rate of prostate cancer death. Since the evidence in this respect is inconsistent, it remains unclear whether the causes of these mortality trends are chance, misclassification, early detection, improved treatments, or a combination of effects.
The incidence of distant-stage prostate carcinoma was relatively flat until 1991 and then started declining rapidly. This decline probably was caused by the shift to earlier stage disease associated with the rapid dissemination of PSA screening. This stage shift can have a fairly sizable and rapid impact on population mortality, but it is possible that other factors such as hormonal therapy are responsible for much of the decline in mortality. Ongoing randomized clinical trials in the United States and Europe are designed to determine whether a mortality benefit is associated with PSA screening.