The observed narrowing of racial disparities in prostate cancer outcome since the advent of PSA screening is not as large as previously believed.
The observed narrowing of racial disparities in prostate cancer outcome since the advent of prostate-specific antigen (PSA) screening is not as large as previously believed, according to a new study. Much of that narrowing is due to artifacts of screening, meaning the predictable effects of screening on survival that occur even when no real benefit is present.
Historically, black men have prostate cancer mortality rates that are approximately double that of white men, though recent trends have suggested this is changing. “Since the widespread adoption of PSA screening for prostate cancer in the early 1990s, there has been a clear narrowing of the disparities in mortality,” wrote study authors led by Ruth Etzioni, PhD, of the Fred Hutchinson Cancer Research Center in Seattle. “However, it is well known that screening induces artifactual effects, which can inflate observed survival even in the absence of any screening benefit.”
Artifacts of screening include lead time, meaning the time by which screening advances diagnosis, and overdiagnosis, meaning the increase in cases that would not have been diagnosed in a patient’s lifetime without screening. The researchers conducted a modeling study using published data on survival, lead times, and overdiagnosis; they determined the portion of improvement in disease-specific survival that could be explained by those artifacts, and then analyzed the remaining unexplained portion of the improvement as well. The results were published in Cancer.
They found that artifacts of screening explain larger proportions of survival improvement in older patients, among both black patients and all races. For example, black patients age 50 to 54 years had a pre-PSA 10-year disease-specific survival rate of 54.6%; the modeled post-PSA survival rate was 70.7%, compared with an actual survival rate of 89.7%, and 46% of the improved survival was due to artifacts of screening. For black patients age 75 to 79 years, 98% of the improvement seen was due to artifacts of screening. This was similar in all races, with 51% explained by screening artifacts in the younger group and more than 100% explained by screening artifacts in the older group.
Also, screening explains much of the narrowing in disparity in outcome. For the group of patients age 50 to 54 years, the pre-PSA disparity was 11.6% in terms of 10-year survival; the post-PSA disparity was only 2.0%, but 35% of that was explained by artifacts of screening. For the group of 75 to 79 year olds, the disparity dropped from 13.7% to 9.0%, but 69% was explained by screening artifacts.
“We do not dispute that long-standing racial disparities in prostate cancer survival may be narrowing,” the authors wrote. “However, the real survival improvement during the PSA era is more modest than observed. Understanding the age-specific and race-specific patterns of screening artifacts on disease-specific survival trends is a necessary prerequisite if we are to use these trends to develop prostate cancer screening policies that are appropriate for black men and for the general population.”