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The Prostate 31:142 (1997)
RESPONSE TO EDITORIAL COMMENTS
The critique of our work is appreciated, and the
author makes some valid points, which I shall address. First, there is concern that we have changed the
emphasis of the test from 95% specificity to 95% sensitivity. We chose to emphasize sensitivity (and, thus,
cancer detection) for many of the reasons Dr. Littrup
brings up, e.g., increased mortality among African
American men (AAM) from prostate cancer and the
possible increased biologic potential of prostate tumors in this cohort. He also points out that we came
up with a similar 95% sensitive value for Caucasian
men (CM). These values are shown in Table I of our
paper.
The author states that the positive predictive value
(PPV) would be a more interesting parameter, insofar
as it is due to the higher incidence of prostate cancer
among AAM. However, any cutoff values chosen for
prostate specific antigen (PSA) will have a higher PPV
among AAM than CM (as Bayes’ Theorem predicts).
Obviously, the PPV for any given value is a function of
the number of true positives (TP) and false positives
(FP). Of course, the values of TP and FP are in turn
determined by the sensitivity and specificity of a given
test (in this case, the cutoff values for PSA) and the
incidence of the disease among the population tested.
As the author points out, focusing only on maximizing the PPV would decrease screening costs (by
decreasing further testing), but at the cost of potentially increasing false negatives (missed cancers). He
then proposes a compromise by using a low cutoff
value for high-risk groups (which would emphasize
sensitivity and cancer detection) and a higher cutoff
value for lower risk groups (which would emphasize
© 1997 Wiley-Liss, Inc.
specificity and decrease false positives). This we have
done by publishing age-specific ranges for AAM (a
high-risk group) that emphasize sensitivity. Dr. Littrup is concerned that in calling these values age specific we are misleading our readers, insofar as we are
proposing test values that emphasize sensitivity rather
than specificity.
His proposal that we use PSA values of 2 ng/ml or
greater for high-risk groups and 4 ng/ml or greater for
lower risk groups, while disregarding age-related differences, has exactly the same potential of misleading
readers who may not realize that the lower value emphasizes sensitivity while the higher one emphasizes
specificity. We believe that our audience will understand that the word specific refers to age in this highrisk group, and that our values do not emphasize
specificity over sensitivity. Our published values have
the advantage of including age as a variable. The decision to screen for prostate cancer is still controversial
and screening should be discussed on an individual
basis. We believe that physicians will appreciate agespecific values to tailor their screening methods as
much as possible to the individual patient.
David G. McLeod, MD, JD, FACS
Chief, Urology Service
Department of Surgery
Walter Reed Army Medical Center
Washington, DC
Uniformed Services University of
the Health Sciences
Bethesda, MD
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