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Recent Changes in Michigan’s Prostate Cancer Incidence: What Does It Mean?
-John T. Wei, M.D.,
-Robert Wood Johnson Clinical Scholar, American Foundation for
Urologic Disease Scholar, and Lecturer in the Section of Urology,
Department of Surgery
Rod Hayward, M.D.,
Director, Veteran Affairs Center for Outcomes Research, Ann
Arbor, and Associate Professor, Department of Internal Medicine
and School of Public Health
The Controversy
Prostate cancer remains among the most controversial health
issues facing men today. An estimated 334,500 new cases will
be diagnosed in the United States in 1997 with an associated
mortality of 41,800 (1). The incidence of prostate cancer
has slowly risen from 1965 to 1985, but beginning in the late
1980s, an epidemic of cases occurred (2). This has been attributed
to the introduction of serum prostate specific antigen (PSA)
as a diagnostic test for prostate cancer. The obvious explanation
for this epidemic is that the use of PSA detects more cancers
than digital rectal examination alone; (3, 4) however, other
factors such as an increased public awareness leading to more
diagnostic testing may also play a significant role. The medical
community continues to debate the issue of screening for prostate
cancer with PSA and whether it will lead to improved survival
(5, 6).
Time Trends in Michigan
Since 1987, prostate cancer has been the leading site of cancer
among men in the state of Michigan. These findings are especially
pertinent to physicians in Michigan where the mortality rate
from prostate cancer in African-American men is higher than
Caucasians (7) and ranks among the highest in the world (8).
In 1985, the Michigan Department of Community Health started
a state-wide cancer registry of all cases of prostate cancer.
This data has reflected national trends in the incidence of
localized, regional and metastatic disease (figure 1). What
can be clearly seen is an abrupt increase in the incidence
of localized cases starting in 1990 and peaking in 1992. This
is followed by an equally sharp drop in the incidence up to
1995. The incidence for regional disease also experienced
a similar phenomena but to a lesser degree, and metastatic
cases actually decreased by 51%. The explanation, of course,
is that there has been a significant stage-shift for this
disease from extra-prostatic to localized cases (figure 2).
However, it should be noted that the incidence for both localized
and extra-prostatic cases has not fallen below pre-PSA levels.
Clinical Relevance
What is the clinical relevance of these epidemiological data?
Certainly, one view, albeit an optimistic view, is that the
incidence of extra-prostatic disease in Michigan will continue
to fall to levels below what it was in 1987 when PSA was introduced.
This would appear to be intuitive since it has been shown
that prostate cancer can be cured when localized (9), however,
caution should be used in this interpretation. A significant
drop in the incidence of extra-prostatic disease has not yet
been demonstrated, and more importantly, the mortality rate
has remained unchanged (figure 3). In order for a stage-shift
to result in decreased mortality, curative treatment has to
be given for cases of localized cancer that would ultimately
lead to death. Simply reporting changes in survival for men
with prostate cancer is misleading due to lead- and length-time
bias (10). Lead-time bias is an apparent increase in survival
due to earlier detection and without alteration of the natural
history of the disease. Length-time bias is the “over-diagnosis”
of less aggressive cases that would never have led to a prostate
cancer death. To date, evidence of benefit from the use of
PSA eludes us.
However, if extra-prostatic cancers continue to fall to levels
below that observed in the pre-PSA era, this would provide
preliminary evidence of benefit. Along with this, we would
expect mortality rates to fall eventually, provided that curative
treatment is being given to at-risk patients. PSA testing
will soon be covered by Medicare at a tremendous cost to health
care. It is incumbent on the medical profession to provide
proof that the use of PSA test leads to lower mortality.
Current Investigation
How can we demonstrate a benefit from the use of PSA if the
mortality rate remains unchanged? The gold standard technique
is to perform a randomized control trial using PSA, but it
will likely take a decade or more before such a study would
yield results. Investigators at the University of Michigan
Comprehensive Cancer Center hope to find early evidence of
benefit by detecting a decrease in the proportion of extra-prostatic
disease in men who undergo screening with PSA. Using a case-control
study design, 500 men with extra-prostatic prostate cancer
at the time of diagnosis will be identified and age-matched
to 500 control men without extra-prostatic disease. An analysis
of the screening rate (exposure) will reveal if there has
been a significant drop in the proportion of extra-prostatic
disease, which would lead to an improved survival benefit.
Results from this study should be available within one to
two years.
References
- Parker SL, Tong T, Bolden S, Wingo PA. Cancer statistics,
1997. Ca: a Cancer Journal for Clinicians. 47(1):5-27, 1997.
- Demers RY, Swanson GM, Weiss LK, Kau TY. Increasing incidence
of cancer of the prostate. The experience of black and white
men in the Detroit metropolitan area. Archives of Internal
Medicine. 154:1211, 1994.
- Catalona WJ, Smith DS, Ratliff TL, Basler JW. Detection
of organ-confined prostate cancer is increased through prostate-specific
antigen-based screening. JAMA. 270:948, 1993.
- Jacobsen SJ, Katusic SK, Bergstralh EJ, Oesterling JE,
Ohrt D, Klee GG, et al. Incidence of prostate cancer diagnosis
in the eras before and after serum prostate-specific antigen
testing. JAMA. 274:1445, 1995.
- Hall RR. Screening and early detection of prostate cancer
will decrease morbidity and mortality from prostate cancer:
the argument against. European Urology. 29 Suppl 2:24, 1996.
- Brawer MK. Screening and early detection of prostate cancer
will decrease morbidity and mortality from prostate cancer:
the argument for. European Urology. 29 Suppl 2:19, 1996.
- Pienta KJ, Demers R, Hoff M, Kau TY, Montie JE, Severson
RK. Effect of age and race on the survival of men with prostate
cancer in the Metropolitan Detroit tricounty area, 1973
to 1987. Urology. 45:93, 1995.
- Muir CS, Nectoux J, Staszewski J. The epidemiology of
prostatic cancer. Geographical distribution and time-trends.
Acta Oncologica. 30:133, 1991.
- Lepor H, Kimball AW, Walsh PC. Cause-specific actuarial
survival analysis: a useful method for reporting survival
data in men with clinically localized carcinoma of the prostate.
Journal of Urology. 141:82, 1989.
- Russel L., Educated Guesses Making Policy about Medical
Screening Tests. University of California Press; 1994.
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