In 1981, a novel transforming gene called neu, related to, but distinct from, the c-erbB protooncogene, was identified (1 -3 ). In 1985, two groups independently isolated identical erbB -related genes from human DNA that they called HER-2 (4 ) and c-erbB-2 (5 ) located at chromosome band 17q11.2 and encoding a 185,000 Dalton tyrosine kinase (2 ,4 ). Studies conducted on human breast cancers showed 28% to have amplified HER2/neu present (7 ) and it was suggested that amplification or increased protein expression might confer a selective advantage (6 ). Over the last ten years, many studies have confirmed the value of using overexpression or amplification of the HER2/neu gene as a predictor of poor outcome in cases of breast cancer (7 -9 ). Clinical trials are currently underway using anti-HER2/neu in an attempt to destroy malignant breast cells (10 ,11 ).