Miguel Srougi
Early detection of prostate cancer
Departamento
de Cirurgia da Faculdade
de Medicina da USP
1. W hy prostate cancer screening should be perform ed.
P rostate cancer w as, until recently, less frequent than
lung and colon neoplasm s. It becam e the m ost frequent
can-cer in m ales from 1990 on (l). It is estim ated that 8 - 10% of
the m ale population w ill develop prostate cancer and 3% w ill
die from it. It is a phenom enon of obvious clinical relevance
(2). F urtherm ore, the rate of occurrence of this neoplasm has
been increasing in the last years for reasons w hich are still
unaccounted for. T here are estim ates indicating that betw een
year 1980 and 2000, the num ber of prostate cancer cases and
consequently deaths from it w ill grow in the 90% range (3). If
one considers the annual expenses for the diagnosis and treat-m ent of prostate cancer cases in the U nited S tates of A treat-m erica,
this sum is in the U $ 12 billions range (4). H aving m entioned
that, it is obvious the m edical, socio-econom ic im portance
of prostate cancer and the interest it rises in the layperson and m edical com m unity.
T he purpose for the introduction of prostate program s
for the early detection of prostate cancer is grounded on the
fact that only in the early stages of the disease, it can be
suc-cessfully cured and that Juring this sam e early stages of the
disease, there are clinical m anifestations. T he use of radical
surgery or radiotherapy achieve a 50 to 85% cure rate in the
cases of localized neoplasm w hereas the anti-androgen
therapy, usually em ployed for the patients w ith m ore advanced
disease, slow s dow n the disease progression w ithout elim
i-nating the neoplasm (I).B ecause only 30 to 50% of the
pros-tate cancer cases are identified in the early stages of the
dis-ease, this early detection through screening program s
repre-sents the only w ay to im prove the prognosis of the prostate cancer patients.
2. P atient selection for the screening program s.
T he prostate cancer is very uncom m on before age 50
unless w hen there is a fam ily history for the disease or for
breast cancer (5). M oreover, in m any cases the neoplasm
show s an indolent progression rem aining in a quiescent state
w ithout producing clinical m anifestations or death of the
pa-tient (1). T his accounts for the discrepancy betw een the m
a-terialization of prostate cancer in autopsy studies and its clini~ cal m anifestations. F or instance, in 80 year-old m ales, the rate
of occurrence of prostate cancer in autopsy studies and the
incidence of its clinical m anifestations are respectively 44%
and 28% (1). T he system atic investigation for prostate
can-cer in advanced aged subjects is controversial because in a
large num ber of these patients, the identification and
treat-m ent of the disease are not necessary (4).
In sum m ary, the group of patients w ho benefit from an early prostate cancer diagnosis are those subjects aged 50 to 70 w ith a life prognosis of at least 10 years (2).
3. M ethods for prostate cancer early detection.
P rostate cancer can be diagnosed in its early stages by
m eans of anal digital touch exam ination, m easurem ent of the
specific prostatic antigen and by m eans of an trans-rectal
ul-trasound (l ,2,4,6,7,8)
D igital R ectal E xam ination (D R E ) w hen perform ed by
an experienced exam iner, allow s the detection of m asses about 0.5 centim eter in diam eter. T his is useful in term s of the clini-cal point of view . S tudies by M c N eal et al have dem onstrated
that the potentially aggressive tum ors have alw ays at least
one cubic centim eter in volum e (9, 10) and a m ass of this size is easily detectable during a D R E . H ow ever, this m ethod fails
in neoplasm s w hich are originated in the transitional in the
transitional zone (periurethral). T hese tum ors account for
nearly 25% of all cases of prostate cancer.
M easurem ent of the specific prostatic antigen in the
serum (S P A ) represent another alternative in the prostate can-cer detection. T he addition of the S P A to the D R E enhances
in 50% the chances of diagnosing prostate cancer (II). A
ddi-tionally, w hen one considers the P S A alone in levels above to
4.0ng/m l (T andem -R P S A , H ybritech) the presence of
p r o s ta tis , h y p e r p la s ic n o d u le s , o r p r o s ta te c y s ts ( 1 2 ) .I n th e
ta b le d e p ic te d b e lo w , th e s e n s ib ility , s p e c if ic ity in d e x e s f o r
th e P D T , P S A a n d T R U S in th e d ia g n o s is o f p r o s ta te c a n c e r
a r e lis te d . A s s h o w n in th e ta b le , th e e m p lo y m e n t o f e a c h o f
th e s e m e th o d s a lo n e a llo w d e te c tio n o f a s m a lle r p e r c e n ta g e
o f th e c a s e s . T h e r e f o r e , ta k in g in to c o n s id e r a tio n , th e c o s ts I
a n d b e n e f its o f e a c h m e th o d , s o m e g u id e lin e s f o r th e e a r ly
p r o s ta te c a n c e r h a v e b e e n e s ta b lis h e d . I n itia lly , a P D T c o m
-b in e d w ith P S A . T h e T R U S is e m p lo y e d o n ly o f b o th P D T
a n d P S A a r e a b n o r m a l ( 1 ,2 ,5 ) . ta te c a n c e r is c o n f ir m e d in n e a r ly 2 5 % o f th e c a s e s . S e v e r a l
o f th e s e c a s e s d is p la y u n r e m a r k a b le P D T a n d u ltr a s o u n d
( 6 ) .N o n e th e le s s , th e e m p lo y m e n t o f P S A a lo n e is in s u f f ic ie n t
f o r th e c lin ic a l d e te c tio n o f e a r ly p r o s ta te c a n c e r b e c a u s e 2 1
to 4 3 % o f th e p a tie n ts w ith d e f in ite ly d ia g n o s e d p r o s ta te c a n
-c e r s h o w a n o r m a l s e r u m le v e l o f th is m a r k e r ( P S A ) ( 2 ) .T h e
p r o s ta te in v e s tig a tio n b y m e a n s o f a n tr a n s - r e c ta l u ltr a s o u n d
s tu d y ( T R U S ) r e p r e s e n t a n o th e r m e th o d to d ia g n o s e lo c a l
n e o p la s m s . T R U S u s u a lly d e m o n s tr a te s a n in c r e a s e d e c h o in
c o m p a r is o n w ith th e h e a lth y p r o s ta te p a r e n c h y m a ( 1 2 ) . T R U S
a llo w s th e d e te c tio n o f m a s s e s o f 7 m m in d ia m e te r a n d u p .
T h is r e n d e r s th e T R U S a b n o r m a l in 8 5 % o f th e c a s e s w ith
p r o s ta te c a n c e r ( 2 ) . T h e in c o n v e n ie n c e o f T R U S is th e o c c u r
-r e n c e o f f a ls e p o s itiv e s w h ic h r e n d e r s its s p e c if ic ity lo w e r
a n d th e r e f o r e its p r e d ic tiv e v a lu e . T h is is o b s e r v e d in n e a r ly
2 /3 o f th e p a tie n ts a n d it is d u e to th e p r e s e n c e o f in f a r c ts ,
M e t h o d s
P D T
S e r u m P S A
T R U S
S e n s ib ilit y
6 9 - 8 9 %
5 7 - 7 9 %
3 6 - 8 5 %
S p e c if ic it y
8 4 - 9 8 %
5 6 - 6 8 %
4 1 - 7 9 %
P o s it iv e p r e d ic t iv e v a lu e
2 6 - 3 5 %
4 0 - 4 9 %
2 7 - 3 6 %
