HercepTestTM (DAKO A/S, Glostrup, Denmark) is an immunohistochemical assay that 
detects HER2/neu gene products, and evaluates the overexpression status of the 
HER2/neu protein in determining eligibility for the Trastuzumab (HerceptinR, 
Genentech, San Francisco, CA, USA) therapy. However, practically, interobserver 
variability of the HER2/neu interpretation of the immunostained results has 
caused marked disagreement with regard to the intensity of tumor staining. In 
this study, we quantitated HER2/neu expression by image analysis, and applied 
this analyzing system to help to minimize interobserver variability of the 
interpretation of the HercepTestTM. All the immunostained results were scored 
semiquantitatively on a range of 0 to 3+ in accordance with the criteria 
described as per the manufacturer's instructions, and quantitatively evaluated 
using an image analyzing system with image processing software. Among the 92 
cases, 15 were scored as 3+, six were 2+, and 32 were 1+ under intraobservers 
agreement. When the cases were quantitated, a high correlation was shown between 
the signal area extracted by image analysis and the corresponding score of 
staining intensity with the HercepTestTM. By converting the quantitatively 
extracted data into a scoring system based upon the criteria, the outcome 
demonstrated a strong concordance with the scoring data obtained from 
immunostaining. The results indicated that a quantitative scoring system 
performed by simple image analysis may provide to improve interobserver 
agreement of the interpretation of the HercepTest TM in clinical practice.