Interpretation of Prostate Needle Biopsies
Case 2, 3A, 3B, 3C -
An Approach to the Diagnosis of Limited Cancer with Prudent Utilization of Immunohistochemical Markers to Resolve the Diagnosis (continued)
Rajal Shah and Ming Zhou
Immunohistochemistry for Differential Diagnosis of Prostate Cancer|
Immunohistochemistry has been widely used in work-up of difficult prostate biopsies (for review, see
). It is used in two clinical settings. First, to distinguish prostate cancer from benign mimics.
Basal cell markers (high molecular weight cytokeratin (HMWCK, CK903), p63) and
alpha-metheyacyl-CoA-racemase (AMACR) are used for this purpose. Second, to differentiate poorly
differentiated prostate cancer from transitional cell carcinoma, colonic adenocarcinoma and other
metastatic carcinoma .
Prostate specific markers (prostate specific antigen (PSA) and prostate
specific acid phosphatase (ASAP)), P501S (protein), cytokeratins (CK7, CK20, CK903) and p63 are used for
this purpose .
Prostate basal cell markers
Antibodies to HMWCK are the first, and the most widely used, basal cell markers
constitute the cytoplasmic intermediate filaments, and are detected by several antibody preparations,
including 34betaE12 (which includes antibodies against cytokeratins 1, 5, 10 &14), cytokeratins 5/6
and cytokeratin 14. These antibody preparations stain the cytoplasm of prostate basal cells.
P63, a p53 homolog, is a nuclear antigen that is expressed only in the prostate basal cells .
Because they target different antigens in basal cells, 34betaE12 and p63 can be used in the same
immunostain reaction as basal cell cocktail to improve the detection of prostate basal cells
use of antibody cocktail is also advantageous over either antibody used alone on prostate biopsies where
the focus in question is often small and may be present only on one slide.
The diagnostic utility of basal cell markers rely on the fact that basal cells, therefore basal cell
markers, are absent in prostate cancer. Prudent use of these markers has profound impact on the
interpretation of prostate biopsies. Basal cell markers can be used to resolve atypical diagnoses and
establish definitive cancer diagnosis in biopsies
They are particularly helpful in the diagnosis
of pseudohyperplastic, foamy and atrophic prostate cancer, as these morphological variants often have
deceptively bland H&E morphology and are difficult to diagnose in biopsy with limited material if
basal cell markers are not used.
Several studies have compared the diagnostic utilities, including the sensitivity and specificity, of
different basal cell marker preparations. In general, these basal cell markers have similar clinical
utility, although the basal cocktail is slightly better than p63, and p63 is superior to HMWCK in
diagnostic sensitivity, especially in TURP specimens with significant cautery artifact
choice of basal cell marker is the matter of the preference and experience of individual laboratories.
P63 and cocktail are routinely used in our laboratories.
There are several diagnostic pitfalls one needs to be aware of when using and interpreting the basal
cell markers to aid the diagnosis of prostate cancer. Basal cell markers can occasionally be absent in
noncancerous lesions for several reasons. HMWCK is susceptible to formalin fixation with progressive
loss of immuno-reactivity with prolonged fixation time . There is a centrifugal decrease of HMWCK
staining in benign glands, with stronger staining in central and larger glands, and reduced, fragmented
or even absent staining in smaller peripheral glands . Benign conditions, including adenosis and
partial atrophy, often have patchy and incomplete basal cell staining
Staining may even be
absent in some glands. High-grade PIN often demonstrates fragmented basal cell staining .
Therefore, when evaluating basal cell immunostains, one has to study the benign glands on the same slide
as internal positive control and accept a negative stain as truly "negative" only when the benign glands
on the same slide are positive for basal cell markers.
AMACR is a tumor marker that is preferentially over-expressed in prostate cancer
It is a key
enzyme in the metabolism of branched chain fatty acids and bile acid intermediates. AMACR can be
detected immunohistochemically with two different antibodies, a monoclonal antibody (P504S), and a
polyclonal one . Currently, the majority of the laboratories use P504S, because this is the antibody
commercially available. Nevertheless, the two antibodies are quite comparable in terms of diagnostic
sensitivity and specificity
The over-expression of AMACR is not only limited in prostate
cancer. It is also expressed in other tumors, including adenocarcinomas of colon, lung, breast, and
papillary renal cell carcinoma .
A typical positive AMACR staining pattern in prostate cancer cells is apical granular. However, AMACR
expression can also be detected by immunohistochemistry in morphologically benign glands, although it is
not known whether these morphologically benign glands with AMACR expression have undergone pre-neoplastic
transformation. However, it does raise the question as to what should be considered as positive AMACR
staining diagnostically. Jiang et al  considered any strong and circumferential luminal AMACR
staining as positive . We, on the other hand, define positive AMACR staining as the staining that is
significantly stronger than that of adjacent benign glands . For example, a prostate cancer with
strong and circumferential AMACR staining will be considered negative if the adjacent benign glands have
similar strong and circumferential staining. In contrast, a prostate cancer with weak apical staining
will be considered positive for AMACR if the adjacent benign glands are completely negative.
The expression of AMACR in prostate cancer is often not uniform. Even within the same lesion, some
glands have strong, some have weak, yet others have negative AMACR staining. Some of the morphological
variants of prostate cancer, including foamy gland, pseudohyperplastic, and atrophic cancer, are less
often to be positive and have weaker staining in cancer glands . Overall AMACR is positive in
approximately 80% of prostate cancer in needle biopsies . Therefore, a positive staining supports a
cancer diagnosis and a negative staining in suspicious focus may not exclude a cancer diagnosis.
Expression of AMACR is also found in a variety of other non-cancerous lesions, including up to 26% of
benign glands, 15-27% of adenosis
3% of partial atrophy , and 35-58% of nephrogenic adenoma
and majority of high-grade PIN
. The AMACR expression in these lesions is in general weak
to moderate. However, it reinforces the notion that positive AMACR does not equate to prostate cancer.
Recently, several antibody cocktails have been formulated for the diagnosis of prostate cancer in
biopsy. The diagnostic utility of basal cell cocktail has been discussed
AMACR and basal cell
markers could be combined in single immunostaining reaction
This cocktail can simultaneously
stain both benign and cancer glands. Benign glands are positive for basal cell marker and negative for
AMACR, and cancer glands are positive for AMACR and negative for basal cell marker. This cocktail has
several advantages over individual antibodies used alone. The biggest advantage is the conservation of
tissue. For limited cancer in needle biopsies, the diagnostic material might be present only in one
section; therefore, not enough for two separate immuno stains. In addition, it is more economical to
combine two immunostaining reactions in one. The disadvantage is that the commercial antibody cocktail
is pre-diluted, and the laboratories could not titrate the antibodies according to their own protocols.
It is important to know that immunohistochemical tests for prostate cancer should not be used as a
screening test. Rather, it should be applied to selected cases whose differential diagnosis includes
prostate cancer based on H&E examination. Interpretation of immunostaining should be in the context
of H&E morphology. On H&E slide one should clearly define which glands are benign, and which
glands are atypical. And for atypical glands, are they suspicious for cancer or are they more likely to
represent benign mimickers of prostate cancer? Immunohistochemistry then can be performed to support or
verify one's H&E impression. A diagnosis should never be established exclusively based on
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