The 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, or antibodies labeled with therapeutically 
useful radionuclides or toxins. This is especially the case when the tumor cells 
are resistant to chemotherapy and tyrosine kinase inhibitors. Studies concerning 
the expression of these receptors in prostate cancer vary in the literature, 
possibly due to differences in patient inclusion, sample preparations and 
scoring criteria. In our study, EGFR, HER2 and HER3 expression was analyzed in 
prostate cancer samples from primary tumors and corresponding lymph node 
metastases from 12 patients. The expression of HER2 and EGFR was scored from 
immunohistochemical preparations and the HercepTest criteria (0, 1+, 2+ or 3+), 
while HER3 expression was scored as no, weak or strong staining. There were 5 
EGFR-positive (2+ or 3+) primary tumors and 6 EGFR-positive lymph node 
metastases, and there was EGFR upregulation in one metastasis. Only 4 of the 12 
patients had marked HER2 expression (2+ or 3+) in their primary tumors and there 
was one downregulation and 5 cases of upregulation in the metastases. Thus, a 
total of 8 out of 12 analyzed metastases were HER2-positive. Of the 12 primary 
tumors, 9 expressed HER3 while only 2 of the lymph node metastases expressed 
recognizable HER3 staining, so 7 metastases appeared to have downregulated HER3 
expression. In one of the primary tumors there was positive co-expression of 
EGFR and HER2, while this co-expression was observed in 4 of the metastases. 
Thus, 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. The results are encouraging for 
studies involving more patients. Possible strategies for EGFR- and HER2-targeted 
therapy are briefly discussed in the present study, especially with regard to 
the expression and co-expression of EGFR and HER2 in metastases.