BOSTON – One of
today’s most contentious medical debates centers on cancer screening, the
benefits of which seem anything but debatable. Indeed, earlier detection, many
believe, logically must give patients an advantage in fighting the disease. In
fact, the evidence does not always support this assumption. Prostate cancer is
a case in point.
Screening entails the mass testing of individuals of a certain age and
gender, regardless of family history or personal health, to identify a
potential disease state. For screening to be useful, the test or procedure must
readily identify the disease in question, and the subsequent treatment must
result in some measurable benefit. In other words, the screened population must
be better off than the non-screened population.
For some health issues – such as
elevated cholesterol – screening yields positive results: a simple blood test
measures the amounts of good and bad cholesterol in the blood, making it easier
to detect related cardiovascular disease, which could lead to heart attacks or
strokes. Those who are screened, diagnosed, and treated experience a lower rate
of cardiovascular events.
Screening for prostate cancer, too,
requires a blood test – the prostate-specific antigen (PSA) test. Elevated PSA
levels would suggest the presence of prostate cancer, even if no physical
abnormalities were detected, so a tissue biopsy would be conducted. At this
point, a diagnosis can be made. If positive, cancer treatment, such as surgery
or radiation, will follow. And, one hopes, the individual will be cured.
Supporters of screening argue that it
helps to detect and treat cancer earlier, when the chances of curing it are
highest. Moreover, younger patients, at least, can better withstand the side
effects of cancer treatment. Proponents also contend that the two-decade
decline in the overall incidence of deaths from prostate cancer is the result
of increasingly widespread PSA testing. Indeed, they encourage more vigorous
screening programs.
But screening’s benefits are not as
straightforward as supporters claim. To be sure, at-risk men – for example,
those with a family history of prostate cancer, African-Americans, or men with
enlarged prostates who are treated with 5-alpha-reductase inhibitors (whose
failure to lower PSA levels could reflect increased risk of developing prostate
cancer) – may want to consider getting tested.
For most healthy men, however, the
United States Preventive Services Task Force (USPSTF) – a leading independent
panel of experts on prevention and primary care – has publicly recommended
against widespread PSA tests. Several well-managed, randomized, long-term human
trials have shown almost no survival benefit for those who are screened,
diagnosed, and treated, compared to those who were never screened.
Of the studies cited by the USPSTF,
one, conducted in Europe, showed a minor benefit in a
subset of men, with no significant quality-of-life improvement. Another,
conducted in the US,
showed no evidence that PSA screening improved prostate-cancer survival rates.
In addition, a recent study comparing outcomes for patients whose prostate
gland was surgically removed to those for patients who underwent only
observation found no differences in survival rates between the two groups.
Moreover, cancer treatment often
carries serious side effects – including urinary incontinence, erectile
dysfunction, and, in those who undergo radiation, inflammation of the lower
rectum or bladder, as well as underreported effects like fecal incontinence –
that can negatively affect patients’ quality of life. Given that many patients
diagnosed with prostate cancer as a result of the PSA test would never suffer
any symptoms, such consequences are difficult to justify.
Yet many refuse to give up screening.
Given this, an active surveillance program could be the best way to address the
most serious consequence of excessive screening: premature, overly aggressive
treatment.
In an active surveillance program, a
patient diagnosed with a PSA-prompted biopsy delays treatment. Instead, he is
closely monitored with various follow-up tests. Only when signs indicate that
the cancer is becoming dangerous is treatment initiated. While this approach is
still being studied, the results so far appear promising: men who participate
in active surveillance programs are 14 times more likely to die of a cause
unrelated to prostate cancer.
As evidence tilts the balance away
from widespread PSA testing, a new screening test or biomarker is urgently
needed that can distinguish effectively between potentially life-threatening
prostate cancers and less dangerous forms. Likewise, less risky treatments are
crucial.
Active surveillance programs are an
encouraging prospect for minimizing the negative consequences of PSA testing.
But, without vastly improved screening practices, prostate cancer screening is
unlikely to help – and can even do serious harm.
Marc B. Garnick is Clinical Professor of Medicine at Beth Israel
Deaconess Medical Center, Harvard Medical School.