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1365
HER2 Expression in Androgen-Independent Prostate
Cancer. David M Reese, Eric J Small, Frederic M Waldman,
Karen Chew, Daniel Sudilovsky, UCSF/Mount Zion Cancer Ctr, San
Francisco, CA.
In contrast to human breast cancer, the frequency and prognostic
significance of HER2 protein expression in prostate cancer remain
controversial. Recently it has been suggested on the basis of in
vitro experiments [Craft et al, Nature Med 1999;5:280] that HER2
expression may be upregulated in the transition from
androgen-dependent (AD) to androgen-independent prostate cancer
(AIPC). To determine the rate of HER2 protein expression in AIPC, we
performed immunohistochemistry (TAb 250 antibody) on 22
paraffin-embedded tissue specimens from patients with AIPC. Included
in this series were 18 TURP specimens, 3 soft tissue metastases, and
1 bone metastasis. HER2 expression was detected in 6 cases (27%): 3
cases had 1+ (low-level) membranous expression, 1 case had 2+
(intermediate) expression, and 2 cases had 3+ (high-level)
expression. The two cases with high-level expression were a TURP
specimen and bone metastasis. Of interest, in the 2 cases where
matched AD and AI tissue specimens were available from the same
patient, there was loss of HER2 expression in the AIPC state. These
data suggest that while membranous HER2 protein expression is found
in a subset of AIPC tumors, the presence of high-level expression is
uncommon. HER2 gene amplification is currently being analyzed by
FISH on these specimens.
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