Baseline PSA and prostate cancer-specific mortality
Posted Jul 12 2010 12:00am
It is well understood that a diagnosis of prostate cancer does not necessarily imply that the patient will ever have progressive disease let alone that he will die of prostate cancer. Indeed, the number of men in America who die of prostate cancer today is believed to be significantly less than three for every 100 men diagnosed.
However, a recent analysis of long-term data from Duke Medical Center does suggest that the baseline PSA level of a patient subsequently diagnosed with prostate cancer (i.e., his PSA level at the time of his first PSA test) may be highly relevant to his personal risk of prostate cancer-specific mortality.
The new paper by Tang et al. (in concert with information in a media release from Duke Medical Center) reports that the Duke Prostate Center database was used to identify men who had their PSA level measured over the past 20 years. The available data were used to show the following:
The database included 4,568 men diagnosed with prostate cancer after a baseline PSA measurement.
The median age of these patients was 65 years at the time of initial PSA testing.
The median baseline PSA was 4.5 ng/ml.
The average (mean) follow-up period was > 9 years.
3.5 percent of the men died from prostate cancer during the study period; > 20 percent died from other causes.
A baseline PSA of ≥ 10 ng/ml was 11 times more likely to be associated with prostate cancer-specific mortality than a baseline PSA level of < 2.5 ng/ml.
A baseline PSA level between 4.0 and 9.9 ng/ml was three times more likely to be associated with prostate cancer-specific mortality than a baseline PSA level of < 2.5 ng/ml.
An advanced age at baseline PSA and African American race were associated with a higher death rate from prostate cancer and death from all causes.
Now it is worth emphasizing a specific point related to this study. It only applies to men who are actually diagnosed with prostate cancer.
This study does not address information about the PSA levels of all the other men who may have been seen at Duke in the same 20-year timeframe and who had a PSA level that may have been elevated as a consequence of prostatitis, or benign prostatic hyperplasia, or trauma, or any other possible stimulus. Thus, we cannot simply say that a baseline PSA level of ≥ 4 ng/ml places a man at heightened risk for prostate cancer-specific mortality. We have to be clear that what this study tells us is that a baseline PSA of ≥ 4 ng/ml in a man who is subsequently diagnosed with prostate cancer increases that man’s risk for prostate cancer-specific mortality by comparison with a baseline PSA of < 2.5 ng/ml.
The critical learning issue here seems to be that early detection of the cancer is key to the potential to minimize the risk of prostate cancer-specific mortality. It should not simply be assumed that early detection of a PSA of ≥ 4 ng/ml in an inevitable signal of heightened risk for prostate cancer-specific mortality.
It is also worth bearing in mind that the data accumulated in this study do go back 20 years. In those 20 years a lot has changed, the average baseline PSA level of 4,500+ men diagnosed today would probably be significantly lower, for example, than the median baseline PSA of the men in this study, because 20 years ago most men didn’t get baseline PSAs in their early 50s (or younger). Indeed, in this study the median age at the time of the baseline PSA test was 65! So time may have an important impact on how to interpret these data with accuracy.