Question: Is the monoclonal antibody Trastuzumab (Herceptin) of potential use in the treatment of prostate cancer?

Context:
Herceptin is widely used in treating Her2-overexpressing breast cancer. However, the application of Herceptin in prostate cancer is still controversial.
Our data demonstrate that Re-188-labeled Herceptin effectively inhibited the growth of DU145 cells compared to the Herceptin- and Re-188-treated cohorts. This implies that targeting Her2 by both radio- and immuno- therapy might be a potential strategy for treating patients with androgen-independent prostate cancer.
epidermal growth factor receptor (EGFR) family members are potential targets for therapy using extra-cellular domain receptor binding agents, such as the antibodies trastuzumab and cetuximab
 there were tendencies for upregulation of HER2, increased co-expression of EGFR and HER2 and downregulation of HER3 in the prostate cancer lymph node metastases in comparison to the primary tumors. 
We performed a comparative analysis in vitro and in vivo of the antitumor effects of three different antibodies targeting different epitopes of ErbB2: Herceptin (trastuzumab), 2C4 (pertuzumab) and Erb-hcAb (human anti-ErbB2-compact antibody), a novel fully human compact antibody produced in our laboratory. Herein, we demonstrate that the growth of both androgen-dependent and independent prostate cancer cells was efficiently inhibited by Erb-hcAb. The antitumor effects induced by Erb-hcAb on some cell lines were more potent than those observed for either Herceptin or 2C4.
These findings suggest that a systemic delivery of 212Pb-trastuzumab could             be an effective modality for management of advanced human prostate cancer.
Human epidermal growth factor receptor type 2 (HER2) overexpression supports proliferation of androgen-independent prostate cancer (PC)
Radiolabeled ABY-025 Affibody molecule provides higher contrast in imaging of HER2-expressing PC xenografts than radiolabeled trastuzumab. 
These studies indicate that dual EGFR/HER2 inhibition, administered together with AWT, sensitize prostate cancer cells to apoptosis during AWT
The overall goal of these studies is to determine whether dual inhibition of the receptor tyrosine kinases epidermal growth factor receptor (EGFR) and HER2 would prolong the effectiveness of this treatment in prostate cancer. 
The expression of HER2 was demonstrated and quantified in all three tested prostate cancer cell-lines.
Such features would definitely favor the use of radiometal labels for trastuzumab and, most likely, for affibody molecules
our data demonstrate that Her2 plays an important role in the support of AR protein stability in the transition of androgen requirement in prostate cancer cells. We hope these findings will provide novel insight into the treatment of hormone-refractory prostate cancer.
These two cell lines exhibited distinct responses to Her2 activation (by heregulin treatment) on Her2 phosphorylation and Her2 inhibition (by AG825 or Herceptin treatments) on proliferation
 While prostate cancers that express high levels of HER-2 are resistant to the killing effects of trastuzumab, they can be targeted for selective gene expression and destruction by lentiviruses with envelope proteins engineered to bind to this therapeutic antibody
Overexpression of ErbB-2 and EGFR has been associated with aggressive disease and poor patient prognosis in a range of human tumour types (e.g. breast, lung, ovarian, prostate
Various approaches have been developed to target the ErbB signalling pathways including monoclonal antibodies (trastuzumab/Herceptin
The data from these in vitro and in vivo studies supported advancement of radiolabeled trastuzumab into two clinical studies
Tumor targeting was evaluated in mice bearing subcutaneous (s.c.) xenografts of colorectal, pancreatic, ovarian, and prostate carcinomas.
we found that although prostate cancers that express high levels of HER-2 are resistant to the killing effects of trastuzumab, they can be targeted for selective gene expression and destruction by viruses with envelope proteins engineered to bind this antibody
detection of prostate cancer (PCa) and advances in hormonal and chemotherapy treatments have provided great clinical benefits to patients with early stages of the disease.
MAbs directed to established targets include those approved for other solid tumors, including anti-human epidermal growth factor receptor-2 (HER2) MAb trastuzumab
We conclude that Her2/neu expression in the peripheral blood mononuclear cell fraction of prostate cancer patients is frequent and therefore this assay may potentially be useful to detect the presence of micrometastatic disease in men with prostate cancer and for monitoring patients enrolled in trastuzumab-based therapeutic protocols.
This study suggests that the docetaxel/trastuzumab combination may prove an effective therapeutic approach for HER2-expressing hormone-refractory prostate cancer.
there was no significant difference in antimetastatic activity between the emulsion and the immunoemulsion despite the affinity of the immunoemulsion towards the HER2 receptor. 
a targeted drug delivery system based on cationic emulsion covalently linked to anti-HER2 monoclonal antibody (Herceptin), in a well-established in vivo pharmacologic model of metastatic prostate cancer that overexpresses the HER2 receptor
The finding of strong, consistent HER-2/neu expression in ACBCC suggests that treatment with Herceptin (trastuzumab) may be effective in patients with this rare tumour.
Although HER2 can be over-expressed in prostate cancer, there is no clinical data to support the use of trastuzumab for prostate cancer patients.
whereas the effect of the trastuzumab-RT combination was inferior to that predicted by the individual effects.
HER 1-2 targeting of hormone-refractory prostate cancer by ZD1839 and trastuzumab
Trastuzumab (Herceptin) as a single agent demonstrated poor efficacy in treating HRPC.
To investigate the efficacy and toxicity of the antibody to the HER-2/neu receptor (trastuzumab, Herceptin) in the treatment of advanced hormone-refractory prostate cancer (HRPC)
Conclusions regarding the predictive value of HER-2 status on outcome after trastuzumab-based therapy were not reached and were only drawn after larger-scale screening efforts. 
rastuzumab plus docetaxel in HER-2/neu-positive prostate carcinoma
clinical trials are currently in progress in patients with prostate cancer testing novel agents that selectively interfere with these receptors, such as trastuzumab,
ytotoxicity of human prostate cancer cell lines in vitro and induction of apoptosis using 213Bi-Herceptin alpha-conjugate
The clinical interpretation of c-erbB-2 abnormalities should reflect the complexity of c-erbB-2 mediated regulatory pathway and explain why tumours with overexpression/amplification of c-erbB-2 very often do not respond to therapy using Herceptin
HER-2 overexpression also has been reported in up to 60% of patients with hormone-refractory prostate carcinoma (HRPC) and was correlated with shortened survival
Unlike breast carcinoma and contrary to prior reports, HER-2 overexpression by IHC in archival prostate tissue from patients who eventually developed hormone-refractory disease was infrequent. There did not appear to be any correlation between HER-2 overexpression by IHC and shed HER-2 antigen levels in serum by ELISA in this tumor type.
Further development of trastuzumab for the treatment of patients with metastatic prostate carcinoma is not feasible until more reliable and practical methods of sampling metastatic disease are developed to identify patients with HER-2 positive tumors.
the expression of ERBB2 in prostate cancer is relatively low, and is not altered during disease progression. Thus, it is unlikely that treatment modalities relying on the overexpression of ERBB2 gene will be useful in treating prostate cancer.
A phase I study was designed to evaluate docetaxel/estramustine plus trastuzumab, a humanized monoclonal antibody that binds to the HER2 receptor, in patients with metastatic androgen-independent prostate cancer (AIPC)
Laboratory evidence also supports the clinical evaluation of docetaxel-based combinations that include agents such as trastuzumab and/or estramustine
trastuzumab, a monoclonal antibody binding to the HER2 receptor; immunotoxin conjugates use an antibody directed against EGFR joined to a cell toxin. All are in clinical trials for a number of cancers, including prostate cancer
we investigated the antitumor efficacy of Herceptin, a new recombinant humanized anti-HER2/neu antibody, which exhibits cytostatic activity on breast and prostate cancer cells that overexpress the HER2 oncogene.
trastuzumab was found to have additive and synergistic effects with some chemotherapeutic agents
ER-2/neu as a therapeutic target in non-small cell lung cancer, prostate cancer
in these prostate cancer model systems, Herceptin alone has clinical activity only in the androgen-dependent tumor and has at least an additive effect on growth,
anti-HER2 receptor monoclonal antibody Herceptin significantly enhanced growth inhibition of the MDA PCa 2a cells.

Answer: Although is still controversial, Trastuzumab (Herceptin) can be of potential use in the treatment of prostate cancer overexpressing HER2, either alone or in combination with other drugs.
Exact answer: yes