The HER2/neu oncogene is overexpressed in human pancreatic cancer, but the 
clinical significance of that overexpression is uncertain. In the present study 
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. That antibody may 
retard tumor growth in certain patients with those diseases. We quantified HER2 
expression in various human pancreatic cancer cell lines and studied the 
bioactivity of this antibody both in vitro and in vivo. Growth inhibition by 
Herceptin was observed in vitro in cell lines with high levels of HER2/neu 
expression. Cell lines with low levels of this protein did not respond 
significantly to the antibody. In vivo we studied two different pancreatic 
cancer cell lines in an orthotopic mouse model of the disease. Herceptin 
treatment suppressed tumor growth in the MIA PaCa-2 tumor cell line, which 
expressed high levels of HER2/neu. These data suggest that Herceptin treatment 
of patients with pancreatic cancer who express high levels of the HER2/neu 
oncogene may be reasonable.