Distinguishing benign prostate glands from malignant ones, based purely on morphology,
on prostatic core needle biopsy specimens (PNBs) may prove difficult, particularly
if the suspicious focus is small. In recent years, several immunohistochemical markers,
including the basal cell cocktail (BCC), 34betaE12 and p63, and the prostate cancer
(PCa) biomarker alpha-methylacyl-CoA-racemase (AMACR), have been used as adjuvants
to morphology, in these diagnostically challenging cases. We prospectively address
the diagnostic utility of using the BCC, in combination with the commercially available
AMACR monoclonal antibody, P504S, on PNBs that required immunohistochemistry (IHC)
studies to make a diagnosis. The goals of this prospective study were to assess the
day-to-day practice in an academic setting, to determine how often these IHC tests
were used on routine PNBs, and to establish how often a combination of the BCC and
P504S were helpful in diagnosing prostate cancer. A total of 772 prospectively collected
PNB cases were examined over a 7-month period. IHC staining was performed in 171 cases
(22%); 123 cases were stained with the BCC in addition to the commercially available
monoclonal AMACR antibody. In 86 of these 123 cases (70%), both stains contributed
to the final diagnosis: PCa in 44 cases, benign in 33 cases and high-grade prostatic
intraepithelial neoplasia in 9 cases. Of the remaining 37 cases (30%), 18 were called
benign or PCa, based solely on appropriate staining with the BCC, with AMACR being
noncontributory because the focus of interest had been cut through (12 cases), there
was negative staining with AMACR (in 4 PCa cases), or there was positive staining
with AMACR (in 2 benign cases showing atrophy). Nineteen of 37 cases were diagnosed
as atypical small acinar proliferation. In these 19 cases either the focus had been
cut through on one or both of the stains (11 cases), both AMACR and BCC failed to
work (2 cases), AMACR was positive in the presence of patchy BCC staining (1 cases),
AMACR was negative in the absence of BCC staining (3 cases), or despite appropriate
staining the focus consisted of 1 gland and was considered too small to call carcinoma
(2 cases). Additional IHC stains were performed in 171 of 772 cases; of these, 123
had sufficient material to perform both the BCC and P504S. The BCC when used in combination
with AMACR rendered a diagnosis in almost 70% of cases. Using these stains in combination
may be a better approach in diagnostically difficult cases as it increases the likelihood
that a definitive diagnosis can be rendered while decreasing the likelihood of an
equivocal diagnosis. However, a limitation of this approach is the loss of tissue
in these small lesions, suggesting that combining AMACR and the BCC on a single slide
would be superior to using either marker separately.