BACKGROUND/AIMS: Evaluation of Her2/neu expression in the peripheral blood 
mononuclear cell fraction of prostate cancer patients by RT-PCR may afford an 
opportunity for the detection of circulating tumor cells and thus serve as a 
marker of micrometastatic disease.
METHODS: We studied Her2/neu expression by reverse transcriptase-polymerase 
chain reaction in peripheral blood mononuclear cell fraction samples of 21 
controls and serially in 43 patients with prostate cancer.
RESULTS: None of the 21 controls expressed Her2/neu whereas 23.25% (95% CI, 
11.75-38.63) of the patients were positive at entry into the study, and 65.11% 
(95% CI, 49.07-78.99) of them had at least one positive result during the 
follow-up period. Her2/neu positivity at study entry did not correlate 
significantly with PSA level, Gleason score, clinical stage or time to PSA 
progression. When we analyzed only patients with advanced disease, we observed a 
trend towards a shorter time to PSA progression in patients with at least one 
positive Her2/neu result during the follow-up (log-rank test, P = 0.08).
CONCLUSIONS: 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.