Laboratory Testing for HER2/neu in Breast Carcinoma: An Evolving Strategy to Predict Response to Targeted Therapy

Nils M. Diaz, MD, Interdisciplinary Oncology Program at the H. Lee Moffitt Cancer Center & Research Institute at the University of South Florida, Tampa, Florida. Submitted July 1, 2001; accepted August 9, 2001

Cancer Control. 2001;8(5) 

In This Article

HER2/neu Status as a Predictor of Response to Targeted Therapy

In any given case, the key determinant of the utility of a test for HER2/neu is whether it is predictive of a patient's response to targeted therapy, which presently consists of trastuzumab. Review of the results using the clinical trials assay (CTA), an immunostaining procedure that employs monoclonal antibodies directed against HER2/neu, suggests that most patients with a beneficial clinical response to Herceptin had tumors with the highest levels of HER2/neu overexpression: 3+ in a 0-3+ scoring system.[4] Unless 2+ positive overexpression of HER2/ neu was confirmed by FISH assay for gene amplification, the probability of a therapeutic response was 0% in second-and third-line monotherapy. Some recent studies also suggest that FISH may be a better predictor than IHC of response to Herceptin.[17,18] Such results have contributed to proposals that FISH should serve as the front-line test for selecting patients for Herceptin therapy. In contrast, Seidman et al[19] found that IHC was as effective as FISH as a predictor of response to Herceptin. The predictive value of IHC and FISH may prove to vary according to how anti-HER/new therapy is used in monotherapy and in combination with nontargeted chemotherapeutic agents.

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