PURPOSE: 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).
MATERIALS AND METHODS: Eighteen patients with HRPC were recruited for this phase 
II trial in which they received trastuzumab for 12 weeks or until disease 
progression or unacceptable toxicity was documented. HER-2 receptor 
overexpression was evaluated using immunohistochemistry (IHC) and dual-color 
fluorescence in-situ hybridization (FISH) assays.
RESULTS: Trastuzumab as a single agent demonstrated little efficacy in treating 
HRPC. Two patients demonstrated stable disease based on a decrease in PSA level 
to less than 50% of baseline. No patient demonstrated a regression of 
radiographic bony or soft tissue metastatic disease. The medication was well 
tolerated in 16 patients (89%), and 2 patients (11%) had to be hospitalized for 
cardiac complications.
CONCLUSIONS: Trastuzumab (Herceptin) as a single agent demonstrated poor 
efficacy in treating HRPC. Based on promising results in treating breast cancer 
with regimens using Herceptin and cytotoxic agents, a similar combination 
approach might demonstrate better efficacy in treating HRPC.